s 

L. 

t, 

X. 

t 

t 

t 

t 

J 

I 

i 

:t 

•» 

l 

1 

4 

-1 

t 

J 

I 

-T 

3! 

•I 

'« 

1 

< 

i 

i 

* 

r 

ti 

>; 

I! 

c 

i] 

i 

( 

s 

j 

3 

! 


J 

l 

( 

! 

< 

I 


Digitized  by  the  Internet  Archive 
in  2017  with  funding  from 
Getty  Research  Institute 


https://archive.org/details/wondersofscienceOOmayh_O 


I 

i 


.T.  r . t . i .1.1 .1. i . v. 


THE 


WONDERS  OF  SCIENCE; 


OK, 


YOUNG  HUMPHRY  DAVY 

(THE  CORNISH  APOTHECARY’S  BOY,  WHO  TAUGHT  HIMSELF  NATURAL 
PHILOSOPHY,  AND  EVENTUALLY  BECAME  PRESIDENT 
OF  THE  ROYAL  SOCIETY). 


lE'tli  lift  nf  rt  fPimittrfttl  3,'ntf 


WRITTEN  FOR  BOYS. 


r. 


/ 


BY 


HENRY  MAYHEN 


& 


’-‘piv 


AUTHOR  OF  “THE  STORY  OF  THE  PEASANT-BOY  PHILOSOPHER,”  ETC. 


Majestic  steep  ! ah,  yet  I love, 

With  many  a lingering  step  to  rove, 
Thy  ivied  rocks  among ; 

Thy  ivied,  wave-heat  rocks  recall 
The  former  pleasures  of  my  soul. 
When  life  was  gay  and  young. 


Enthusiasm — Nature’s  child — 

Here  sung  to  me  her  wood-songs  w i!d. 

All  warm  with  native  tire; 

I felt  her  soul-awakening  flame. 

It  hade  my  bosom  burn  for  fame, 

It  hade  me  strike  the  lyre.” 


Davy’s  Ode  to  St.  Michael's  Mount  in  Corntrall.  Written  at  the  age  of  19. 


1ST  E W Y ORK: 

HARPER  & BROTHERS,  PUBLISHERS, 

PEARL  STREET,  FRANKLIN  SQUARE. 

1856. 

•f.  ewi-rs  W 


A WORD  OR  TWO 


BY  WAY  OF 

EXPLANATION  AND  DEDICATION 

TO 

MICHAEL  FARADAY. 


My  dear  Sir,- — 

* I inscribe  your  name  on  one  of  the  fly-leaves  of 
this  little  book,  with  the  same  devotion  as  youths 
are  wont  to  carve  upon  the  trunk  of  some  forest 
tree  the  name  of  those  whom  they  admire  most  in 
the  world ; and  I do  so  for  many  reasons. 

First  of  all,  because  Davy  was,  as  it  were,  the 
foster-father  of  your  great  genius ; and,  secondly, 
because  it  allows  me  to  tell  the  lads  for  whom  this 
book  has  been  written  the  graceful  story  of  the  way 
in  which  the  hero  of  it  first  befriended  you- — the 
young  “ bookseller’s  apprentice,  very  fond  of  experi- 
ment, and  very  averse  to  trade” — -in  your  own  dig- 
nified language ; and,  moreover,  because  I know 
your  zeal  in  the  cause  of  education,  and  that  you 
are,  like  all  generous  minds  when  fired  with  the 


VI 


PREFACE. 


beauty  of  fine  truths  and  discoveries,  unable  to  rest, 
as  it  were,  till  you  have  imparted  them  to  others, 
and  so  made  them  as  happy  as  yourself  with  the 
wondrous  knowledge.  Indeed,  it  is  the  glorious 
privilege  of  intellectual  pursuits  that  they  are  not 
marked  by  that  “ selfishness,”  which  made  you  as  a 
boy  “ desirous  of  escaping  from  trade for  wisdom, 
happily,  can  share  its  riches  with  the  world,  and  yet 
be  all  the  richer  for  the  sharing.  None  know  better 
than  yourself  that  every  science  is  built  up  of  an  in- 
finity of  such  contributions ; and  that,  had  the  hu- 
man mind  been  impressed  with  a desire  to  hoard  its 
intellectual  gains — to  keep  them  locked  in  the  cof- 
fers of  the  brain — how  little  even  you — who  have 
added,  by  your  many  profound  discoveries,  more  to 
the  knowledge-fund  of  the  world  than  any  other  sin- 
gle philosopher — could  yourself  have  known.  There 
is  no  finer  instance,  perhaps,  of  human  magnanimity 
than  the  chemist  working  unseen  in  his  laboratory-— 
watching  alone  for  hours  the  action  of  different  kinds 
of  so-called  dead  matter  upon  each  r)thp.r1  in  fhp  hnpp 
of  being  able  to  add  his  little  mite  of  truth  to  that 
store  of  mental  riches,  which  is  to  benefit  not  only 
his  own  generation,  but  all  those  to  come  for  ages  aft- 

er.  Nor  can  we  detract  from  the  natural  greatness 
of  the  act  by  ascribing  it  to  any  lower  principle  of 
our  soul — such  as  that  petty  craving  for  praise  which 
we  call  “ vanity”  in  women,  and  a desire  for  fame 
among  poets  and  philosophers;  for  every  true  scien- 


PREFACE. 


V1L 


tific  mind  knows  that  there  is  sufficient  reward  in 
{he  intense  beauty  of  a new  discovery — the  first  flash 
across  the  brain  of  some  deep  insight  into  the  mys- 
teries of  Nature — to  repay  him,  over  and  over  again, 
for  all  the  long  puzzling  of  his  thoughts ; and  that, 
were  he  even  alone  in  the  world,  without  a voice  to 
cheer  him  on,  he  must  still  continue  spelling  out  pas- 
sage after  passage  of  the  Great  Poem  of  Creation, 
from  the  mere  love  of  the  Poem  itself. 

I can  readily  understand  that  it  was  some  such 
generous  purpose  that  first  rendered  you  anxious  “ to 
enter  the  service  of  science,  which,”  as  you  say,  you 
“imagined  made  its  pursuers  amiable  and  liberal,” 
for  this  is  impressed  in  every  line  of  the  following 
letter,  which  becomes  peculiarly  interesting  as  a rec- 
ord of  the  circumstances  which  brought  together  two 
of  the  greatest  chemical  geniuses  that  the  world  has 
yet  seen. 

“To  J.  A.  Paris,  31.1). 

“Royal  Institution,  Dec.  23,  1829. 

“ My  dear  Sir, — You  asked  me  to  give  you  an 
account  of  my  first  introduction  to  Sir  H.  Davy, 
which  I am  very  happy  to  do,  as  I think  the  cir- 
cumstance will  bear  testimony  to  his  goodness  of 
heart. 

“ When  I was  a bookseller’s  apprentice,  I was 
very  fond  of  experiment,  and  very  averse  to  trade. 
It  happened  that  a gentleman,  a member  of  the 


PREFACE, 


viii 

Royal  Institution,  took  me  to  hear  some  of  Sir  H. 
Davy’s  last  lectures  in  Albemarle  Street.  I took 
notes,  and  afterwards  wrote  them  out  more  fairly 
in  a quarto  volume. 

“My  desire  to  escape  from  trade,  which  I thought 
vicious  and  selfish,  and  to  enter  into  the  service  of 
Science,  which  I imagined  made  its  pursuers  amiable 
and  liberal,  induced  me  at  last  to  take  the  bold  and 
simple  step  of  writing  to  Sir  H.  Davy,  expressing  my 
wishes,  and  a hope  that,  if  an  opportunity  came  in 
his  way,  he  would  favour  my  views;  at  the  same 
time,  I sent  the  notes  I had  taken  at  his  lectures. 

“ The  answer,  which  makes  all  the  point  of  my 
communication,  I send  you  in  the  original,  request- 
ing you  to  take  great  care  of  it,  and  to  let  me  have 
it  back,  for  you  may  imagine  how  much  I value  it. 

“ You  will  observe  that  this  took  place  at  the  end 
of  the  year  1812,  and  early  in  1813  he  requested  to 
see  me,  and  told  me  of  the  situation  of  Assistant  in  the 
Laboratory  of  the  Royal  Institution,  then  just  vacant. 

u At  the  same  time  that  he  thus  gratified  my  de- 
sires as  to  scientific  employment,  he  still  advised  me 
not  to  give  up  the  prospects  I had  before  me,  telling 
me  that  Science  was  a harsh  mistress ; and,  in  a pe- 
cuniary point  of  view,  but  poorly  rewarding  those 
who  devoted  themselves  to  her  service.  He  smiled 
at  my  notion  of  the  superior  moral  feelings  of  philo- 
sophic men,  and  said  he  would  leave  me  to  the  ex- 
perience of  a few  years  to  set  me  right  on  the  matter. 


PREFACE. 


IX 


“ Finally,  through  his  good  efforts,  I went  to  the 
Hoyal  Institution  early  in  March  of  1813,  as  Assist- 
ant in  the  Laboratory ; and  in  October  of  the  same 
year  went  with  him  abroad,  as  his  assistant  in  experi- 
ments and  in  writing.  I returned  with  him  in  April, 
1815,  resumed  my  station  in  the  Royal  Institution, 
and  have,  as  you  know,  ever  since  remained  there. 

“ I am,  dear  Sir,  very  truly  yours, 

“M.  Faraday.” 

The  following  is  the  note  of  Sir  H.  Davy,  alluded 
to  in  Mr.  Faraday’s  letter: 

“To  Mr.  Faraday. 

“December  24,  1812. 

“ Sir, — I am  far  from  displeased  with  the  proof 
you  have  given  me  of  your  confidence,  and  which 
displays  great  zeal,  power  of  memory,  and  attention. 
I am  obliged  to  go  out  of  town,  and  shall  not  be  set- 
tled in  town  till  the  end  of  January : I will  then  see 
you  at  any  time  you  wish. 

“ It  would  gratify  me  to  be  of  any  service  to  you. 
I wish  it  may  be  in  my  power. 

“ I am,  Sir,  your  obedient,  humble  servant, 

“ H.  Davy.”* 

And  now  let  me  add,  by  way  of  excuse  for  the 
many  short-comings  of  the  present  volume,  that  I 
* Extracted  from  Dr,  Paris’s  “Life  of  Davy,” 


X 


PREFACE. 


have  found  some  little  difficulty  in  developing  my 
object,  which  was  to  show  youths  how  one  of  the 
greatest  natural  philosophers  had,  when  a lad,  like 
themselves,  made  himself  acquainted  with  the  princi- 
ples of  science,  and  thus  to  induce  them  to  “ go  and 
do  likewise for,  assuredly,  there  is  no  education 
like  that  self-education  which  is  sure  to  follow  di- 
rectly a fervent  taste  is  created  for  any  particular 
branch  of  knowledge.  To  create  such  a taste  was 
my  sole  motive  for  writing  this  book.  Nevertheless, 
when  I came  to  deal  with  the  subject,  I discovered 
that  it  was  impossible  to  follow  literally  the  scientific 
history  of  Davy’s  mind,  since  he  had  begun  by  adopt- 
ing the  most  flighty  theories.  To  have  evolved  all 
his  visionary  notions  when  a lad,  in  a work  that  was 
meant' to  have  an  educational  tendency,  would  have 
been  merely  to  have  taught  error.  I have,  however, 
in  adapting  the  book  to  the  present  state  of  science, 
deviated  as  little  as  possible  from  the  biographical 
facts,  and  I have,  moreover,  in  all  things  striven  to 
be  true  to  the  character  of  my  hero,  which  after  all 
is  the  great  truth  required  in  “ story-books.”  Again, 
by  a pardonable  license,  I believe  I have  made  the 
boy  foreshadow  some  of  his  after-discoveries — such 
as  the  safety-lamp — and  for  all  these  deviations  I can 
only  plead  a desire  to  show  youths  that  they  have  it 
in  their  own  power  to  do  as  the  Cornish  apotheca- 
ry’s boy  did,  if  they  will  but  set  about  the  work 
quickened  with  the  same  determination  to  succeed. 


preface. 


XI 


It  is  my  belief  that  our  present  system  of  education 
begets  in  the  minds  of  youths  too  great  a sense  of 
dependence,  and  too  little  reliance  on  their  own  pow- 
ers, so  that  it  is  thought  by  a lad  on  leaving  school 
to  be  impossible  to  learn  any  thing  without  the  help 
of  a master  to  teach  it.  Now  my  object  in  such 
books  as  the  present  is  to  show  boys  that  some  of  the 
greatest  minds  the  world  has  yet  seen  have  been  self- 
taught  ; and  by  letting  the  young  note  how  the  great 
men,  when  they  were  young  too,  set  about  the  task 
of  informing  themselves,  thus  to  breed  in  youthful 
minds  not  only  a faith  in  their  own  capabilities,  but 
a taste  for  the  beauties  of  knowledge,  as  well  as 
a strong  purpose  to  number  themselves,  if  possible, 
among  the  future  teachers  of  mankind. 

And  now,  my  dear  Sir,  let  me,  in  conclusion,  thank 
you  for  your  generous  encouragement  of  my  labours 
when  I was  engaged  in  inquiring  into  the  condition 
of  the  “ London  Poor.”  Many  know  your  wisdom, 
but  none  are  better  acquainted  with  your  goodness 
than 

Yours,  very  truly, 

Henry  Mayhew. 


Bonn,  Nov.  25th , 1854. 


CONTENTS. 


CHAPTER  I. 

PAGE 

The  "Widowed  and  the  Fatherless 15 

CHAPTER  II. 

Young  Humphry’s  Resolves 33 

CHAPTER  III. 

Humphry  and  his  Mother 50 

CHAPTER  IY. 

The  first  Drink  at  the  Well 70 

CHAPTER  Y. 

The  first  Glimmer  of  the  Safety-lamp 93 

CHAPTER  YI. 

The  Wonders  of  Heat  : its  Sources 112 

CHAPTER  VII. 

The  wonderful  Diffusion  of  Heat 134 

CHAPTER  VIII. 

The  wonderful  Effects  of  Heat 193 

CHAPTER  IX. 

The  wonderful  Effects  of  Heat — (continued) 208 


XIV 


CONTENTS. 


CHAPTER  X. 

PAGE 


The  wonderful  Effects  of  Heat — ( concluded ) 241 

CHAPTER  XI. 

Humphry  and  his  “Wonderful  Lamp” 285 

CHAPTER  XII. 

Humphry  Practises  as  a Surgeon — on  himself  ....  315 
CHAPTER  XIII. 

The  first  Sun-Pictures 329 

CHAPTER  XIV. 

The  Wonders  of  the  Refraction  of  Light 341 

CHAPTER  XY. 


The  Wonders  of  the  Refraction  of  Light — ( con- 


tinued)   337 

CHAPTER  XVI. 

The  Wonders  of  the  Reflexion  of  Light 405 

CHAPTER  XVII. 

The  Wonders  of  Colour  and  Photography ....  419 

CHAPTER  XVIII. 

Conclusion 445 


THE  WONDERS  OF  SCIENCE. 


CHAPTER  I. 

THE  WIDOWED  AND  THE  FATI1EKLESS. 

“Well,  gentlemen,  i have  gone  over  your  several 
accounts,  and  find  that  ;Iie  debts  of  the  late  Mr.  Rob- 
ert Davy  amount  altogether  to  the  sum  of  £1300.” 

These  words  were  addressed  to  a little  group  of 
tradesmen  and  others  who  were  assembled  in  a 
small  room  over  a mercer’s  shop,  in  the  town  of 
Penzance.  There  was  Jan  Penberthy,  the  neigh- 
bouring miller,  who,  though  in  his  holiday  clothes, 
had  sufficient  of  the  flour  clinging  to  his  black  eye- 
brows and  whiskers  to  indicate  his  calling;  and 
Malachy  Carteret,  the  carpenter  and  builder,  who 
had  slipped  on  his  best  coat,  as  he  ran  out  from  his 
work,  to  be  present  the  meeting,  and  had  still 
the  brass  ends  of  his  foot-rule  projecting  from  the 
little  fob  at  the  side  of  his  fustian  trousers.  There 
was  Mr.  Trevisky,  too,  the  sporting  lawyer,  in  his 
check  shooting -jacket,  all  over  pockets,  and  those 
at  the  hips  large  enough  for  game  or  law  papers, 


16 


THE  WONDERS  OE  SCIENCE. 


and  who  held  in  his  hand  a square,  horny-looking 
parchment  deed ; and  close  beside  him  sat  the 
village  apothecary,  in  a long,  snuff- brown  great- 
coat, between  the  skirts  of  which  might  be  seen, 
shining  in  the  light,  his  high  boots,  that  reached 
well  up  to  his  knees  ; and  there  were  two  or  three 
other  of  the  village  tradespeople  besides,  all  seated 
at  the  end  of  the  little  apartment,  and  who,  when 
they  heard  the  amount  of  their  united  claims,  ex- 
changed glances  with  one  another  in  astonishment 
at  the  largeness  of  the  sum. 

At  a table  in  front  of  the  little  assembly  sat 
Mr.  John  Tonkin,  the  old  gentleman  who  had 
addressed  them.  Nor  was  he  the  least  remarkable 
among  the  company,  for  he  was  habited  in  the 
costume  that  had  been  fashionable  in  the  previous 
century.  Over  his  shrivelled  and  veiny  hands 
flapped  deep  lace-ruffles,  and  the  top  of  his  head 
was  white  as  a twelfth  - cake,  with  the  large 
powdered  wig  that  surmounted  it.  The  straight, 
stand-up  collar  of  his  Quaker-cut  coat  was  as  if 
mildewed  at  the  back  with  the  powder  that  fell 
from  his  peruke,  and  the  large  fan-like  frill  that 
protruded  from  his  waistcoat — which  was  long  as 
a modern  groom’s — was  speckled  brown  in  places 
with  snuff,  as  thick  as  nutmeg  on  a custard  ; while 
from  underneath  the  table  at  which  he  sat  peeped  a 
pair  of  gold  shoe-buckles  and  black  silk  stockings. 
On  a chair  by  his  side  lay  the  cocked  hat  which 


THE  WIDOWED  AND  THE  FATHERLESS.  17 


completed  his  antiquated  costume,  and  the  under- 
neath part  of  which  was  greyed  with  hair-powder 
and  long  usage. 

Peculiar  as  was  the  old  gentleman’s  dress,  yet  it 
had  more  of  a quaint  than  comical  appearance  with 
him ; for  his  features,  though  creased  with  age,  and 
his  form,  though  slightly  bowed  with  his  load  of 
years,  were  still  of  too  manly  a cast  to  excite  any 
irreverent  feeling,  even  in  the  lightest  minds ; indeed, 
he  had  too  stern  and  austere  a look  to  dispose  any  to 
smile  at  the  oddity  of  his  costume.* 

* Mr.  Tonkin  (says  Dr.  John  Davy,  in  his  Memoirs  of  the 
Life  of  his  brother)  “will  long  be  remembered  in  Penzance, 
both  for  excellences  and  peculiarities.  The  latter  marked  him 
as  a person  of  the  gone-by  time,  and  attracted  the  notice  even  of 
the  careless  observer.  He  held  in  aversion  modern  changes  of 
fashion,  and  in  his  old  age  wore  the  dress  of  his  youth — the 
cocked  hat,  large  powdered  wig,  hand-ruffles,  upright  collar ; in 
brief,  the  professional  dress  of  the  beginning  of  the  last  century 
— and  his  manly  form  and  countenance  suited  well  with  this 
venerable  costume.”  Dr.  Davy  says,  moreover,  that  Mr.  Tonkin 
“held  a distinguished  place  among  his  fellow-townsmen,  being 
looked  up  to  for  his  sterling  worth  and  strength  of  judgment, 
and  very  dear  to  his  friends  for  his  benevolence,  kindness,  and 
very  generous  and  friendly  disposition.”  He  was  “ of  a quick 
temper,”  he  adds,  “but  his  anger  was  of  short  duration.”— See 
Life  of  Sir  Humphry  Davy , vol.  i.  p.  109. 

Sir  Humphry  himself,  in  his  last  letter  to  Mr.  Tonkin,  says, 
“If  I was  nearer  I would  endeavour  to  be  useful  to  you.  I 
would  endeavour  to  pay  some  of  the  debts  of  gratitude  I owe  to 
you,  my  first  protector  and  earliest  friend.  As  it  is,  I must  look 
forward  to  a futurity  that  will  enable  me  to  do  this  ; but  believe 
me,  wherever  I am,  and  whatever  may  be  my  situation,  I shall 
never  lose  the  remembrance  of  obligations  conferred  on  me,  or 
the  sense  of  gratitude  which  ought  to  accompany  them.” 

R 


18 


THE  WONDEKS  OF  SCIENCE. 


After  a short  pause  the  old  gentleman  continued 
his  address  to  the  company  before  him.  “ Now  to 
meet  this  sum  of  £1300  there  is  the  property  of  the 
farm  at  Varfell,  which  is  valued  at  about  £150  a 
year,  and  upon  which  Mr.  Trevisky’s  client  has  a 
mortgage  to  a small  amount.”* 

At  the  mention  of  the  name  of  the  attorney,  that 
gentleman  proceeded  to  open  the  square  deed  before 
him,  and  to  throw  back  the  huge  skins,  that  looked 
like  large  sheets  of  bladder,  as  he  glanced  his  eye 
down  them  one  after  another. 

“ This  little  property,  gentlemen,”  proceeded 
Mr.  Tonkin,  “ is  all  that  the  widow  and  her  five 
children — the  eldest  of  whom,  you  will  permit  me 
to  remind  you,  is  but  sixteen  years  of  age — have  to 
subsist  upon.  Mrs.  Davy,  therefore,  I think,  has  a 
claim  to  some  little  indulgence  and  sympathy  at 
your  hands.  Some  years  must  pass  before  her 
children  are  old  enough  to  obtain  a maintenance 
for  themselves,  and  in  the  mean  time  they  have  to 
be  supported,  educated,  and  apprenticed.  How 
this  is  all  to  be  done  upon  such  slender  means  is  a 
matter  that  I need  not  tell  you  adds  severely  to  the 
widow’s  distress ; for  not  only  has  she  the  grief  to 
bear  on  losing  the  partner  with  whom  she  had  lived 

* “ When  Mrs.  Davy  became  a widow,  she  wras  in  her  thirty- 
fourth  year,  with  five  children,  all  of  whom  were  still  to  be  edu- 
cated, excepting  Humphry,  her  eldest  son.  Her  income  at  this 
time  was  about  £150  a year,  and  it  was  encumbered  with  a debt 
of  £1300.” — Dr.  Davy's  Life  of  Sir  Humphry , vol.  i.  p.  7. 


THE  WIDOWED  AND  THE  FATHERLESS.  19 


in  happiness  for  nearly  twenty  years,  but  she  has 
the  greater  grief,  if  possible,  of  knowing  that  her 
children  are  fatherless,  and  that  she  herself  lacks 
the  means  of  providing  for  them  in  comfort.  Her 
sorrow,  then,  gentlemen,  has  a double  sting.  It 
arises  not  only  from  regret  for  the  past,  but  a dread 
of  the  future.  I am  sure,  therefore,  she  will,  under 
her  great  affliction,  meet  with  every  consideration 
from  you.” 

At  this  point  Mr.  Malachy  Carteret — a little  man, 
remarkable  for  the  blackness  and  bushiness  of  his  eye- 
brows, which  grew  so  close  together  as  to  look  like 
one  long  one,  rather  than  a pair,  and  who,  from  his 
being  considered  a “ good  prayer-maker”  at  the  chap- 
el to  which  he  belonged,  was  always  glad  of  an  op- 
portunity of  displaying  his  oratorical  powers — ven- 
tured to  observe,  that  he  was  sure  all  then  present 
felt  for  Mrs.  Davy  under  her  trials,  but  they  had 
most  of  them  children  of  their  own,  and  it  was  their 
duty  to  look  at  home  first ; for  who  could  tell  how 
soon  they  themselves  might  be  called  away,  and  their 
little  ones  left  in  the  same  distressing  situation,  un- 
less their  bills  were  duly  paid?  “Now  my  little 
account,”  proceeded  the  carpenter,  “ has  been  stand- 
ing so  long  as  the  new  house  at  Yarfell  has  been 
built,  and  that  were  the  same  year  as  Dolly  Pent- 
reath  died — I mean  her  as  were  102  year  old — and 
that’s  some  time  agone,  you  know ; so  I’m  sure  no 
one  can’t  say  as  I’ve  been  hard  about  my  little  mat- 


20 


THE  WONDERS  OF  SCIENCE. 


ter.  But  we  were  a thinking  among  ourselves,  Mr. 
Tonkin,  that  as  you’d  always  been  suchy  kind  friend 
to  the  family,  and  as  we  hadn’t  no  wish  to  trouble 
Mrs.  Davy  under  her  affliction,  that  maybe  a — a — 
you  — you  — you  wudn’t  mind  becoming  security 
yourself  for  the  debts,  and  then  they  cud  stand  over 
for  another  year  or  two  if  need  be.  You’ll  excuse 
ma  making  maself  so  bould,  sir ; but  I’m  a plain 
man,  and  think  plain  speaking  is  better  than  double- 
dealing at  ale  times.” 

The  old  gentleman’s  brow  fell  suddenly,  and 
looking  the  carpenter  full  in  the  face,  he  said, 
scornfully,  “Though  you  have  no  wish  to  trouble 
Mrs.  Davy  under  her  afflictions,  you  would  not 
object,  it  seems,  to  involve  her  friends  in  her  lia- 
bilities. You  allude,  sir,  to  my  past  services,  and 
surely  the  recollection  of  the  melancholy  occasion 
which  rendered  such  services  necessary  should 
have  made  you  less  eager  after  what  is  due  to  you, 
and  less  anxious  to  entangle  in  the  family  diffi- 
culties a person  who,  when  he  found  that  his  assist- 
ance was  needed,  has  never  added  to  the  distress  by 
waiting  till  asked  for  it.  In  this  very  house,  now 
thirty-seven  years  ago,  it  was  my  sad  lot  to  see 
three  young  girls  deprived  of  both  father  and  moth- 
er in  the  same  week.  Mrs.  Davy  was  one,  and 
the  youngest  of  those  three — left  almost  in  her 
infancy  without  a friend  or  counsellor  to  help  her 
through  the  world.  And  now  in  her  womanhood 


THE  WIDOWED  AND  THE  FATHERLESS.  21 


the  same  hard  fate  attends  her — bereft  of  him  whose 
affection  had  made  him  her  protector,  and  finding; 
her  children  fatherless,  as  she  herself  was,  at  the 
very  time  when  needing  most  a father’s  care. 
Surely  the  remembrance  of  a double  bereavement 
like  this,  sir — for  hardly  is  she  out  of  her  orphan- 
age before  she  is  doomed  to  enter  on  her  widow- 
hood— should  teach  you  that  Providence  must  have 
some  special  design  in  visiting  so  much  misery  upon 
this  poor  lady.*  Nevertheless,  I am  happy  to  say 
that  Mrs.  Davy  needs  no  pecuniary  assistance  from 
her  friends,  and  requires  but  little  indulgence  from 
those  to  whom  her  husband  was  indebted.  It  is 
proposed  to  increase  the  mortgage  upon  the  farm 
at  Yarfell  to  the  amount  of  £1300,  though  this — 

* “ Mrs.  Davy  was  the  third  and  youngest  daughter  of  Grace 
and  Humphry  Millett Mr.  Millett  was  engaged  in  busi- 

ness in  the  town  of  Penzance  as  a mercer.  He  and  his  wife  died 
young,  and  in  the  same  week — he  on  the  3d  of  June,  1757,  and 

she  on  the  9th Mr.  John  Tonkin  was  their  friend,  and 

supplied  the  place  of  a father  to  them  (the  orphan  children),  and 
they  retained  through  life  a most  grateful  sense  of  his  kindness, 
and  of  the  great  obligations  they  owed  to  him.  At  the  time  of 
the  death  of  Mr.  and  Mrs.  Millett,  he  (Mr.  Tonkin)  was  residing 
in  their  house  (I  suppose  in  lodgings),  and  there  he  continued  to 
reside  for  some  years,  the  children  being  under  the  care  of  a Miss 
Peggy  Adams,  their  cousin,  in  whose  name  the  mercer’s  business 
was  continued,  by  the  profits  of  which  the  family  was  chiefly  sup- 
ported.”— Dr.  John  Davy,  p.  7,  vol.  i. 

Dr.  Paris,  in  his  life  of  Sir  Humphry  Davy  (p.  2),  says,  speak- 
ing of  the  philosopher’s  mother,  “ Her  maiden  name  was  Grace 
Millett,  and  she  was  remarkable  for  the  placidity  of  her  temper 
and  the  amiable  and  benevolent  tendency  of  her  disposition. 


22 


THE  WONDERS  OF  SCIENCE. 


even  if  Mr.  Trevisky  can  obtain  the  money  at  4 
per  cent. — will  reduce  the  family  income  to  less 
than  £100  a year;  and  immediately  the  mortgage 
is  completed  and  the  money  paid,  your  accounts, 
gentlemen,  will  be  discharged.  The  reason  of  my 
requesting  your  attendance  here  to-day  was  not  to 
seek  to  make  any  compromise  with  you,  nor  to 
crave  any  unusual  indulgence  at  your  hand,  but 
merely  to  ascertain  the  amount  of  the  collected 
claims  against  the  late  Mr.  Davy,  and  to  inform 
you  that  steps  were  being  taken  for  a speedy  pay- 
ment of  them,  so  that  you  might  not  trouble  his 
widow  with  any  importunities  on  the  matter.  She, 
poor  soul,  has  enough  to  bear  with  in  the  privation 
she  has  recently  suffered,  and  those  'wordly  ones 

She  had  been  adopted  and  brought  up  with  her  two  sisters,  un- 
der circumstances  of  affecting  interest,  by  Mr.  John  Tonkin.  . . . 
To  withhold  a narrative  of  the  circumstances  which  led  Mr. 
Tonkin  to  the  adoption  of  these  orphan  children  would  be  to  de- 
prive the  world  of  one  of  those  bright  examples  of  pure  and  dis- 
interested benevolence  which  cheer  the  heart  and  ornament  our 
nature The  parents  of  these  children  having  been  at- 

tacked by  a fatal  fever  expired  within  a few  hours  of  each  other- 
The  dying  agonies  of  the  surviving  mother  were  sharpened  by 
her  reflecting  on  the  forlorn  condition  in  which  her  children 
would  be  left.  For,  although  the  Milletts  were  originally  aris- 
tocratic and  wealthy,  the  property  had  undergone  so  many  sub- 
divisions as  to  have  left  but  a very  slender  provision  for  the 
member  of  the  family  to  whom  she  had  united  herself.”  On  the 
decease  of  Mrs.  Millett  (Dr.  Paris  tells  us),  Mr.  Tonkin  imme- 
diately took  charge  of  her  three  orphan  daughters,  and  “con- 
tinued their  kind  benefactor  until  each  in  succession  found  a 
home  by  marriage.” 


THE  WIDOWED  AND  THE  FATHEKLESS.  2o 

which  threaten  herself  and  children  in  the  future ; 
but,  thank  Heaven,  she  is  prepared  to  meet  all  her 
trials  with  resignation  and  courage.” 

Then,  rising  from  his  seat,  he  bowed  haughtily  to 
the  company  as  he  said,  “Now,  gentlemen,  I wish 
you  a good  day.” 

The  words  were  no  sooner  uttered  than  Mr.  Tre- 
visky,  who  had  previously  folded  up  the  deed,  and 
sat  fidgetting  on  his  chair  for  the  last  quarter  of  an 
hour — now  twisting  a piece  of  red  tape  round  and 
round — then  paring  his  nails — and  then  twiddling 
the  brass  fox’s-head  buttons  of  his  shooting-jacket — 
the  words  were  no  sooner  uttered,  we  repeat,  than 
the  lawyer  started  to  his  feet,  and,  pulling  out  his 
watch,  said,  half  to  himself,  “Egad,  I shall  be  in 
time  for  the  cock-fight  yet ;”  and  then,  waving  his 
hand  rapidly  in  the  air,  shouted  as  he  darted  from 
the  room,  “I’ll  see  to  that  directly,  Mr.  Tonkin — - 
I’ll  see  to  it  directly.” 

Malachy  Carteret  was  the  last  to  leave,  for  he 
purposely  remained  behind  to  plead  his  excuse 
to  Mr.  Tonkin  for  the  use  he  had  made  of  his 
name. 

“I  hope  no  offence,  I’m  sure,  sir,”  began  the  lit- 
tle carpenter.  “ I always  thoft  ma  money  safe  enow, 
but  ya  see  times  is  hard,  and  there’s  the  men  to  pay 
every  Saturday  night,  and  that’s  a great  pull.  No 
one  feels  more  for  Mrs.  Davy  than  your  humble 
servant  M.  C.  does.  Her  husband  always  behaved 


24 


THE  WONDERS  OE  SCIENCE. 


honourable  to  me,  and  M.  C.  is  ‘ ever  grateful  for 
past  favours,’  as  my  card  says.  That  there  wor  a 
bit  of  poor  Mr.  Davy’s  handiwork,  worn’t  it,  Mr. 
Tonkin  ?”  added  Malachy,  pointing  to  the  oak  man- 
tel-piece, that  was  elaborately  and  beautifully  carved 
with  birds,  fruit,  and  flowers. 

“Yes,”  returned  the  old  gentleman,  dryly:  “Mr. 
Davy  presented  it  to  me  when  he  used  to  come 
courting  here,  at  the  time  his  wife  and  her  sisters 
were  under  my  care.” 

“ Ah,  he  wor  very  clever  with  his  tools,”  contin- 
ued the  carpenter.  “ 6 The  last  of  the  carvers,’  we 
used  to  call  him.  I remember  him  afore  he  went  to 
London  to  larn  the  business — he  lived  with  his  uncle 
Robert  then.  I used  to  work  for  the  uncle ; indeed 
I sarved  my  time  with  the  late  Mr.  Davy’s  father — 
the  builder,  ya  know — so,  of  coose,  I cudn’t  mean 
anything  but  kindly  to  the  family — only  money’s 
very  scarce  just  now,  sir,  and  I’ve  a-mashes  of  bills 
to  meet  this  quarter : so  I hope  no  offence,  I hope 
no  offence,  sir.  You  doan’t  want  nothing  in  my 
way,  do  you,  Mr.  Tonkin 

The  old  gentleman  shook  his  head. 

“Very  well,  sir,”  proceeded  the  tradesman; 
“ when  you  do,  M.  C.  will  be  proud  to  take  your 
orders  — ever  grateful  for  past  favours,  sir,  and 
hoping  for  a continuance  of  your  kind  support. 
Allow  me  to  give  you  one  of  my  new  cards,  sir ; 
you’ll  see  I says  as  much  there.”  So  saying,  the 


THE  WIDOWED  AND  THE  FATHERLESS. 


25 


pushing  little  carpenter  thrust  one  of  the  printed 
bits  of  pasteboard  into  the  old  gentleman’s  hand. 

Suddenly  a loud  shout  was  heard  in  the  street 
beneath. 

Malachy  and  Mr.  Tonkin  looked  vacantly  at  one 
another,  as  they  both  inwardly  wondered  as  to  the 
cause  of  the  noise. 

In  a few  minutes  the  shouting  was  repeated,  and 
this  time  the  ear,  quickened  by  curiosity,  could  dis- 
tinguish the  shrill  cries  of  the  village  boys  and  wo- 
men among  the  rest. 

The  carpenter,  in  the  excitement  of  the  moment, 
forgot  his  customary  obsequiousness,  and  rushing  to- 
wards the  window  threw  open  the  little  diamond- 
paned  casement,  making  its  metal  frame  twang 
again  as  he  did  so ; and  as  he  craned  his  neck  over 
into  the  street  he  cried,  “ Oh,  Mr.  Tonkin,  Mr. 
Tonkin!  here,  you  never  saw  suchy  thing  in  ale 
your  life  !” 

The  old  gentleman  was  sufficiently  curious  to  be 
unable  to  resist  sharing  in  the  excitement,  and  pro- 
ceeded to  join  the  little  carpenter,  who  was  still 
eagerly  surveying  the  mob  that  was  gathered  round 
about  the  “Star  Inn,”  on  the  opposite  side  of  the 
street. 

“ It’s  Squire  Giddy’s  new  conveyance,  sir !”  ex- 
claimed Malachy.  “ The  gardener  told  me  last 
night  it  had  come  down  from  London  the  day 
afore,  with  all  its  wheels  done  up  in  haybands 


26 


THE  WONDERS  OE  SCIENCE, 


like  an  Irish  reaper’s  legs.  It’s  the  fust  as  has 
ever  bin  seen  in  these  parts,  and  so  of  coose  the 
whole  town  has  come  to  have  a peep  at  it.” 

Ay,  so  it  had ! All  Penzance  was  out  to  behold 
the  first  carriage  that  had  ever  appeared  in  its 
streets. 

There  were  the  fishwomen  from  the  neighbouring 
villages  of  Mousehole  and  Newlyn,  who  had  stopped 
in  their  rounds  to  join  in  the  throng,  and  who  had 
their  “ cowals  ” or  panniers  of  fish  slung  round  the 
crown  of  their  broad-brimmed  hats,  with  the  load 
of  pilchards  glittering  like  lumps  of  silver  at  their 
backs.  And  there  were  the  ruddy-faced  oil-girls, 
who  had  put  down  their  heavy  pitchers  and  ceased 
for  a while  their  cries  of  “ Buy  ma  traa-in  ! Buy 
ma  traa-in !”  to  eye  “ the  big  box  upon  wheels,” 
as  they  called  it.  The  portly  town -crier,  too,  was 
there,  with  his  huge  dustman -like  bell  turned 
upwards,  and  looking  like  a big  tulip  in  his  hand  ; 
for  having  found  that  his  audience  had  suddenly 
deserted  him,  and  were  more  attracted  by  the  sight 
of  the  new  conveyance  than  with  his  announce- 
ment that  the  grocer  “had  just  received  several 
chests  of  the  best  tea  from  London,”  the  bellman 
had  himself  helped  to  swell  the  crowd,  and  was 
now  as  eager  as  any  to  obtain  a view  of  the  new 
wonder.  Mingling  with  these  might  be  seen  the 
forms  of  the  boatmen — half-smugglers,  half-fisher- 
men— from  the  neighbouring  shore,  with  their  tight- 


t 


THE  WIDOWED  AND  THE  FATHERLESS. 


27 


fitting  blue  “ Guernseys,”  their  yellow,  greasy -look- 
ing, fan-tail  hats,  and  their  large  high  jack-boots, 
that  bagged  about  their  legs  and  looked  as  rusty  as 
if  they  had  been  made  out  of  brown  paper ; whilst 
at  the  outside  of  the  motley  group  the  eye  fell  upon 
the  news-boy,  mounted  on  a podgy  pony,  with  his 
long  tin  horn  in  his  hand  and  pad  of  “ Sherborne 
Mercurys”  under  his  arm ; and  he,  in  his  eagerness 
to  catch  sight  of  the  strange-looking  vehicle,  was 
leaning  over  on  one  side  of  the  saddle,  as  a butcher- 
boy  loves  to  ride.  All  the  shop  people  were  at  their 
doors:  some  in  long  aprons,  and  others  with  white 
sleeves  on  their  arms  over  their  coats ; and  the  boys 
kept  darting  across  from  the  houses  towards  the  mob ; 
while  the  upper  windows  all  down  the  street  were 
knobbed  over  with  heads,  each  bent  towards  the  one 
grand  focus  of  attraction. 

“It’s  a queer-looking  consarn,  aint  it,  sir?”  in- 
quired Malachy;  “and  there’s  a good  bit  a work  in 
it,  I’ve  no  doubt.” 

“ It’s  a hideous  lumbering  affair,”  responded  the 
old  gentleman,  as  he  turned  away  from  the  win- 
dow, “ and  it’s  a great  pity  that  persons  haven’t 
something  better  to  excite  their  admiration  than  the 
follies  of  the  rich ; but  there’s  such  a love  of  lux- 
ury coming  over  our  people,  that  soon  we  shall  be- 
come as  effeminate  as  those  of  the  East,  who  are 
borne  about  upon  couches  when  they  journey  from 
one  place  to  another.  In  times  past  we  were  a 


28 


THE  WONDERS  OF  SCIENCE. 


sturdy,  energetic  race,  inured  to  hardship,  and  lov- 
ing, rather  than  avoiding,  exercise ; but  now  we 
must  have  soft,  easy  seats,  and  beds  of  down,  or  we 
cannot  rest.  Not  many  years  back  the  floors  of 
our  nobles’  houses  were  strewn  with  rushes,  but  at 
present  even  our  gentry  are  beginning  to  find  a 
sanded  room  unpleasant  to  their  feet,  and  so  they 
must  needs  have  soft  carpets  to  tread  upon — as  if 
they  had  all  at  once  grown  as  tender-footed  as  ne- 
groes. There’s  Squire  Austell  has  already  carpet- 
ted  his  best  sitting-room ; and  mark  my  words ! 
there’s  sufficient  of  the  monkey  in  our  natures  to 
make  his  great  and  little  neighbours  ape  the  Squire’s 
manners.  Ugh ! We  shall  be  as  unmanly  as  fid- 
dlers before  many  years  have  passed  over  our  heads. 
Haven’t  we  got  to  drink  slops  for  breakfast  instead 
of  a horn  or  two  of  good  strong  ale,  as  they  did  in 
our  fathers’  time?  and  do  you  think,  sir,  strength, 
and  courage,  and  energy  are  to  be  got  out  of  tea- 
cups ? Soon  we  shall  find  it  impossible  to  eat  with- 
out silver  forks,  as  they  do  in  London  already ; and, 
by  and  by,  the  dinner-bell  will  ring  at  the  same 
hour  as  the  curfew-bell  used  to  toll  in  olden  times 
■ — for  what’s  called  fashion  is  setting  nearer  that 
way  every  day.  But,  thank  goodness,  we  still  dine 
at  noon  here,  and  our  parties  are  limited  to  tea 
and  Pope  Joan  at  three  o’clock,  instead  of  grand 
dinners  or  dances  with  Frenchified  gavottes,  and 
minuets  that  begin  with  the  owls  and  end  with  the 


THE  WIDOWED  AND  THE  FATHERLESS. 


29 


lark.  I hate  such  new-fangled  customs!  they 
would  put  John  Bull  into  stays  like  a Frenchman, 
and  exchange  his  top-boots  for  dancing  pumps. 
Take  my  word  for  it,  sir,  since  that  four-wheeled 
aid-to-laziness  has  appeared  in  our  town  we  shall 
shortly  find  every  one  of  our  would-be  fine  ladies 
unable  to  stir  a yard  from  their  homes  without 
one.”* 

“ You’re  quite  right,  Mr.  Tonkin,  quite  right,  sir,” 
chimed  in  the  little  carpenter ; u our  rich  folk  are 

* “The  state  of  society  in  the  Mount’s  Bay  only  half  a century 
ago,”  says  Dr.  John  Davy,  “ was  peculiar  and  different  from 
what  it  is  at  present.  Cornwall  was  then  without  great  roads. 
The  roads  which  traversed  the  country  were  bridle-paths  rather 
than  carriage  roads.  Carriages  were  almost  unknown,  and  carts 
even  very  little  used.  I have  heard  my  mother  relate  that  when 
she  was  a girl  there  was  only  one  cart  in  the  town  of  Penzance, 
and  if  a carriage  appeared  in  the  streets  it  attracted  universal 
attention.  Pack-horses  were  then  in  general  use  for  conveying 
merchandise,  and  the  prevailing  manner  of  travelling  was  on 
horseback.  In  the  same  town,  where  the  population  was  about 
2000  persons,  there  was  only  one  carpet ; the  floors  of  rooms  were 
sprinkled  with  sea  sand,  and  there  was  not  a silver  fork.  The 
only  newspaper  which  then  circulated  in  the  West  of  England 
was  the  ‘ Sherborne  Mercury,’  and  it  was  carried  through  the 
country,  not  by  the  post,  but  by  a man  on  horseback,  specially 
employed  in  distributing  it Visiting  was  then  con- 

ducted differently  from  what  it  is  at  present.  Dinner-parties  were 
almost  unknown,  excepting  at  the  annual  feast  time.  Christmas, 
too,  was  then  a season  of  peculiar  indulgence  and  conviviality, 
and  a round  of  entertainments  were  given,  consisting  of  tea  and 
supper.  Excepting  at  these  two  periods,  visiting  was  almost 
entirely  confined  to  tea-parties,  which  assembled  at  three  o’clock 
and  broke  up  at  nine,  and  the  amusement  of  the  evening  was 
commonly  some  round  game  at  cards,  as  Pope  Joan  or  Com- 


30 


THE  WONDERS  OF  SCIENCE. 


getting  more  proud  and  fond  of  luxuries  and  vanities 
every  day  of  their  lives.  Why,  what  do  you  think? 
they’re  talking  of  putting  cushions  to  all  the  seats 
of  the  pews  in  our  chapel,  sir,  just  because  the  gen- 
tlefolks has  ’em  to  their  sittings  in  Madern  church ! 
and  I give  you  my  word,  sir,  I’ve  only  just  finished 
setting  a bright  polished  steel  grate  in  the  withdraw- 
ing-room,  as  they  call  it,  at  Castle  Horneck.  It’s 
just  bin  had  down  from  London,  and  I declare  one 
might  see  to  shave  one’s  self  in  any  part  of  it.  It 

merce Amongst  the  middle  and  higher  classes 

there  was  little  taste  for  literature,  still  less  for  science,  and  their 
pursuits  were  rarely  of  a dignified  or  intellectual  kind.  Hunt- 
ing, shooting,  wrestling,  cock-fighting,  generally  ending  in  drunk- 
enness, were  what  they  most  delighted  in.  Smuggling  was  car- 
ried on  to  a great  extent,  and  drunkenness  and  a low  scale  of 

morals  were  naturally  associated  with  it Few  places 

have  exhibited  greater  changes  within  the  last  half  century  than 
Penzance.  Not  a single  family  belonging  to  the  great  gentry 
now  in  existence  west  of  Playle,  or  in  the  Mount’s  Bay,  was 
known  one  hundred  years  ago.” 

“ Carriages,  it  may  be  added,  are  of  French  invention.  Under 
Francis  I.  (a.  d.  1515-1547),  who  was  contemporary  with  our 
Henry  VIII.,  there  were  but  two  in  Paris,  one  of  which  belonged 
to  the  Queen,  and  the  other  to  Diana,  the  natural  daughter  of  the 
French  Henry  II.  There  were  but  three  in  Paris  in  1550  ; Hen- 
ry IY.  of  France  (a.  d.  1589-1610)  had  one,  but  of  very  rude  con- 
struction, and  without  straps  or  springs.  The  first  courtier  who 
set  up  this  equipage  in  France  was  Johnde  Laval  de  Bois-Dau- 
phin,  who  could  not  travel  otherwise  on  account  of  his  enormous 
bulk.  Previously  to  the  use  of  carriages  the  kings  of  France 
travelled  on  horseback,  the  princesses  were  carried  in  litters,  and 
ladies  rode  behind  their  squires.  The  first  carriage  seen  in  En- 
gland was  in  the  reign  of  Mary,  about  1553  ; but  the  art  of  making 
them  was  unknown  in  this  country  at  that  time.  Close  carriages 


THE  WIDOWED  AND  THE  FATHERLESS.  81 

4 

never  was  made  to  put  a fire  in,  I’m  sure.  But 
there’s  nothing  I can  do  for  you  in  my  little  way ; 
is  there,  Mr.  Tonkin  % I’ve  got  the  newest  designs 
for  furniture  just  arrived  from  town  by  the  pack- 
horse  as  came  in  last  Monday.” 

Mr.  Tonkin  shook  his  head,  and  turned  towards 
the  window. 

“ I hope  no  offence,  sir,”  continued  Malachy ; 
u another  time,  maybe,  I shall  be  honoured  with 
your  commands,  and  then  I can  only  say  that  your 

of  good  workmanship  began  to  be  used  by  persons  of  the  highest 
quality  at  the  close  of  the  sixteenth  century  ; Fitz-Allen  earl  of 
Arundel  is  said  to  have  been  the  first  who  used  them,  and  this 
was  in  1580 ; their  construction  was  various.  They  were  first 
made  in  England  about  the  year  1590,  when  they  were  called 
‘ whirlicotes.’  In  the  year  1601,  an  Act  was  passed  to  prevent 
the  effeminacy  of  men  riding  in  carriages  (43d  Elizabeth).  The 
Duke  of  Buckingham,  in  1619,  wras  the  first  who  had  a carriage 
with  six  horses  to  it ; and  the  Duke  of  Northumberland,  on  ob- 
taining his  liberation  from  the  Tower  (where  he  had  been  impris- 
oned since  the  Gunpowder  Plot)  and  hearing  that  Buckingham 
was  drawn  about  with  six  horses  to  his  carriage,  ordered,  out  of 
rivalry,  eight  horses  to  be  put  to  his,  and  in  that  manner  passed 
from  the  Tower  through  the  City.” — Haydn’s  Dictionary. 

“ In  the  twelfth  century  carpets  were  articles  of  luxury.  It  is 
mentioned  by  old  English  historians,  as  an  instance  of  Becket’s 
splendid  style  of  living,  that  his  sumptuous  apartments  were, 
every  day  in  winter,  strewn  with  clean  straw  or  hay.  This  was 
about  the  year  1160.  The  manufacture  of  woollen  carpets  was 
introduced  into  France  from  Persia  at  the  end  of  the  sixteenth 
or  beginning  of  the  seventeenth  century.  Some  artisans,  who 
had  quitted  France  in  disgust,  came  over  to  England  and  es- 
tablished the  carpet  manufacture  among  us  about  1750.  Our 
Kidderminster,  Axminster,  and  Wilton  manufactures  are  the 
growth  of  the  last  hundred  years.” — Ibid. 


32 


THE  WONDERS  OF  SCIENCE. 


orders  shall  be  punctually  attended  to  by  your  hum- 
ble servant,  M.  C. and,  having  delivered  himself 
of  this  speech,  the  pushing  little  carpenter  bowed 
himself  backwards  out  of  the  room. 


I 


CHAPTER  XI. 

young  Humphry’s  resolves. 

“ The  first  and  last  Inn  in  England,  kept  by 
Richard  Botheras,”  was  the  inscription  recorded 
on  both  sides  of  a sign-board  that  swung  backwards 
and  forwards  outside  a little  lonely  homestead — more 
like  a cottage  than  a tavern — standing  at  the  extreme 
western  point  of  Cornwall. 

The  open  door  revealed  a room  without  a visitor  ; 
the  floor  was. white  with  sea-sand,  and  you  could  tell 
at  a glance,  from  the  evenness  with  which  the  sand 
was  strewn,  how  scanty  were  the  customers  in  that 
part  of  the  world,  for  it  was  plain  that  no  foot  had 
trodden  it  that  day.  Above  the  ample  chimney- 
board  was  ranged  a row  of  bright  tin  mugs,  that 
had  been  worn  more  by  polishing  than  use.  The 
top  of  the  little  round  deal  table  that  stood  in  the 
centre  of  the  room  was  as  clean  as  if  it  had  been 
newly  planed  ; and  over  the  painted  chest  of  draw- 
ers, in  one  corner,  stood  what  appeared  like  a quire 
of  tea-boards,  which,  together  with  the  written 
paper  pasted  against  the  wall,  and  informing 

C 


34 


THE  WONDERS  OF  SCIENCE. 


the  stranger  that  “ parties  were  supplied  with 
hot  water,”  gave  one  a notion  of  the  many  visit- 
ors who  came  in  summer  to  take  tea  at  the  Land’s 
End. 

The  host,  from  lack  of  custom,  was  busy  in  the 
garden  at  the  back,  digging  in  refuse  fish  as  manure 
for  his  next  year’s  crop  ; and  the  hostess  might  be 
seen  in  the  adjoining  out-house,  with  her  arms  half 
buried  in  a cushion  of  dough,  preparing  the  week’s 
bread  for  the  humble  family. 

Suddenly  the  innkeeper  paused,  with  his  foot 
resting  on  his  spade.  His  quick  ear  had  caught 
the  clink  of  a horse’s  hoofs  on  the  neighbouring 
granite.  The  man  put  his  hand  across  his  brows, 
and  looked  under  it  in  every  direction  to  see  who 
was  coming. 

In  a minute  or  two  afterwards  he  ran  to  his  wife, 
crying,  “ Come,  tidy  tliaself  a bit,  dame ! Here’s 
Master  Davy  on  his  pony  Derby  jist  at  hand : he’s 
ale  in  deep  black,  too.” 

The  good  wife  was  not  long  in  scraping  the 
dough  from  her  hands,  and,  having  invested  herself 
in  a clean  apron,  was  quickly  at  the  door  beside 
her  husband,  awaiting  the  arrival  of  the  youthful 
visitor. 

As  the  innkeeper  had  stated,  the  lad  was  dressed 
in  deep  mourning,  and  the  beaver  of  his  hat  was 
completely  hidden  by  the  broad  crape  band  that 
encircled  it,  while  the  gloss  upon  his  clothes  indi- 


✓ 





YOUNG  HUMPHRY  S RESOLVES. 


37 


catecl  the  recent  loss  he  had  met  with.  To  a casual 
observer  there  was  but  little  in  the  youth’s  ap- 
pearance  to  mark  the  budding  genius  which  in- 
spired him,  excepting  the  ample  forehead  and  the 
full  black  eyes  beneath  it.  He  was,  however,  gem 
erally  considered  an  “ extraordinary-looking  boy.,; 
He  was  of  diminutive  stature,  while  the  roundness 
of  his  shoulders  gave  him  somewhat — as  it  has  been 
termed  — of  a “bucolic  aspect.”  His  hair  was 
chestnut  brown,  and  hung  in  neglected  curls  about 
his  brow ; his  eyes  were  dark  and  piercing,  but  the 
rest  of  his  features  were  anything  but  finely  chis- 
elled. His  complexion  appeared  paler  than  ordi- 
nary, from  the  contrast  of  the  suit  of  black  in  which 
he  was  habited,  and  the  dejected  air  and  wet-look- 
ing eye  gave  a melancholy  tone  to  his  appearance 
that  immediately  enlisted  the  heart  towards  the 
boy.* 

* “ Davy,  it  may  be  remarked,  possessed,  when  a boy,  a coun- 
tenance which,  in  its  natural  state,  was  very  far  from  comely; 
while  his  round  shoulders,  inharmonious  voice,  and  insignificant 
manner,  were  calculated  to  produce  anything  rather  than  a 
favourable  impression.  In  riper  years  he  was  what  might  be 
called  ‘good-looking;’  although,  as  a wit  of  the  day  observed, 
his  aspect  certainly  was  of  the  ‘bucolic’  character.” — Dr.  Paris' 
Life  of  Sir  I Humphry  Davy , p.  33.  The  Doctor  afterw'ards 
describes  young  Davy  as  an  “ extraordinary -looking  boy.” 
“ His  manners  were  retreating  and  modest,”  says  Mr.  Poole 
(one  of  Davy’s  oldest  friends),  in  a letter  to  Dr.  Paris,  speak- 
ing of  Sir  Humphry  in  early  life;  “he  was  generally  thought 
naturally  graceful,  and  the  upper  part  of  his  face  was  beau- 
tiful. When  he  first  lectured  at  the  Royal  Institution,  the 


38 


THE  WONDERS  OF  SCIENCE. 


The  lad  said  but  a word  or  two  in  answer  to  the 
greeting  of  the  couple,  and  jumping  from  the  saddle, 
gave  the  reins  to  the  innkeeper,  who  forthwith  led 
the  plump  little  animal  round  to  the  stable. 

The  instant  after  the  youth  had  disappeared  among 
the  rocks. 

“Poor  lad!  lie  seems  deeply  cut  up;  doan’t  he, 
Richard  V’  said  the  wife,  following  her  husband  to 
the  shed. 

ladies  said,  ‘ Those  eyes  were  made  for  something  besides  por- 
ing over  crucibles.’  ” — Dr.  John  Davy's  Life  of  his  Brother,  vol. 
i.  p.  136.  “ I was  very  young,”  Lady  Brownrigg  says,  in  a 

letter  to  Dr.  Davy,  “ when  I first  had  the  pleasure  of  seeing 
your  highly-gifted  brother.  We  had  been  invited  bj'  Dr.  Rich- 
ardson to  go  to  his  cottage  at  Portrush,  to  meet  the  famous 
Mr.  Davy.  We  arrived  a short  time  before  dinner;  in  passing 
through  a room  we  saw  a youth,  as  he  appeared,”  (Davy  was 
twenty-eight  years  of  age  at  this  time)  “ who  had  come  in  from 
fishing,  and  who,  with  a little  note-book,  was  seated  in  a win- 
dow-seat, having  left  a bag,  rod,  &c.  on  the  ground.  He  was 
very  intent  on  this  little  book,  and  we  passed  through  unnoticed. 
When  I went  into  the  drawing-room  I felt  some  little  awe  at 
this  great  philosopher,  annexing  to  such  a character,  at  least, 
the  idea  of  an  elderly  grave  gentleman — not,  perhaps,  writh  so 
large  a wig  as  Dr.  Parr,  or  so  sententious  a manner  as  Dr. 
Johnson — but  certainly  I never  calculated  on  being  introduced 
to  the  identical  youth,  with  a little  brown  head  like  a boy,  that 
we  had  seen  with  his  book  at  the  window-seat,  and  who  when  I 
came  into  the  drawing-room  was,  in  the  most  animated  man- 
ner, recounting  an  adventure  which  had  entertained  him  on  the 
Causeway,  and,  from  his  mode  of  telling  it,  was  causing  loud 
laughing  in  the  whole  room.” — Given  in  the  Life  of  Sir  Humphry , 
by  Dr.  John  Davy , who  speaks  of  the  above  account  as  being 
“very  descriptive  of  tire  appearance  and  manner”  of  his  brother 
“ at  this  time.” 


YOUNG  HUMPHRY’S  RESOLVES. 


39 


“ Ah,  that  he  doa,”  returned  Richard,  as  he  stoop- 
ed down  under  the  pony  to  loosen  its  girths.  “ He’s 
not  tha  maze-gerry  hoy  he  was  a little  while  agone, 
when  he  used  to  come  over  here,  Greace,  with  a 
hammer  a cracking  all  the  stones  that  lay  in  his  way 
into  ‘midjons  and  jouds,’  and  scrambling,  like  a 
young  goat,  over  the  rocks  after  some  trumpery  bit 
of  stone  as  took  his  fancy — -just  as  our  Jan  do  after 
daws’  eggs.” 

“Yes,  that  he  used  to,”  returned  the  wife,  tak- 
ing olf  her  clean  apron,  and  carefully  folding  it 
up  as  she  talked ; “ and  I’ve  seed  Master  Hum- 
phry come  back,  after  being  out  all  day  among 
the  rocks,  with  his  cap  full  of  old  stones,  as  he 
seemed  to  prize  like  as  if  they  was  lumps  of  goold, 
but  such  as  I wodn’t  a picked  out  of  4 a stomps’ 
— not  I.  Ah ! there’s  sad  trouble  at  Yarfell  now, 
take  my  word  for  it,  Richard.  Mistress  Davy,  poor 
thing ! has  seen  enough  sorrow  in  her  time  to  ha’ 
broke  many  a stout  heart ; and  here  she’s  left  with 
five  young  ones,  and  not  a 4 cheeld-vean’  among 
’em  as  can  get  a penny  to  help  her.  Master  Hum- 
phry’s a good  scholard,  they  say ; but  laming  won’t 
fill  the  cupboard,  Dick ; and  they  tells  me,  down 
at  Penzance,  that  Mr.  Davy  (rest  his  soul !)  was  too 
fond  of  wasting  his  money  in  mines — as  we’ve  seen 
many  a family  ruined  with  in  our  day  — to  leave 
his  wife  anything  to  fall  back  upon  at  this  time ; 
though  I’m  sure  I pity  the  poor  widow  and  her 


40 


THE  WONDERS  OF  SCIENCE. 


little  ones  from  the  bottom  of  my  heart,  for  it  isn’t 
none  of  their  bringings  on.  Sometimes,  do  you 
know,  Dick,  I fancy  as  there’s  a spell  on  that  poor 
woman.” 

u Go  along  with  you  and  your  spells !”  indig- 
nantly shouted  the  husband,  as  he  held  the  pail 
of  water  for  the  pony  to  drink  from ; u you’ve 
always  got  some  stuff  of  that  kind  in  your  head, 
Greace.” 

u Well,  you  may  talk  as  you  like,  but  I shall 
b’lieve  in  such  things  to  my  dying  day,”  retorted  the 
superstitious  little  body.  u Didn’t  I go  to  Madera. 
Well  and  drop  some  pins  into  it ; and  didn’t  they  fali 
with  their  pints  together,  I should  like  to  know? 
And  wasn’t  our  old  sow  took  ill  the  very  week  after- 
wards, and  died  on  the  very  day  as  we’d  settled  to 
kill  her — eh  ? Oh  ! you’re  as  unb’lieving  as  a Jew  ; 
you  are,  indeed,  Dick.” 

The  innkeeper  treated  his  wife’s  argument  with 
a hearty  laugh,  whereupon  the  dame  proceeded  to 
cite  to  him  a hundred  and  one  such  instances  as  were 
current  throughout  the  county,  and  in  the  midst  of 
which  we  must  leave  the  worthy  couple  for  the  pres- 
ent. 

The  restless,  pensive  boy,  had  wandered  to  the 
extreme  point  of  the  land,  and  here,  resting  upon 
a shelf  of  crag  far  above  the  sea,  that  roared  and 
dashed  against  the  base,  he  sat  for  a while,  with 


YOUNG  HUMPHRY’S  RESOLVES. 


41 


his  tearful  eye  peering  across  the  Atlantic,  vacantly 
gazing  at  the  huge  watery  disc  that  heaved  like  a 
giant  breast  before  him.  Behind  the  lad  towered 
tremendous  pinnacles  of  granite,  some  with  their 
monster  blocks  ranged  in  cubes  one  above  the 
other,  like  Nature’s  solid  masonry ; others  with 
massive  stones  standing  right  on  end  ; while  some 
seemed  tossed  about  in  such  confusion  as  if  the 
“ sixth  seal”  itself  had  opened,  and  the  heavens 
had  rained  rocks  upon  the  land.  Here  a large 
square  lump  protruded  like  a bond-stone  from  the 
straight  sides  of  some  tall  pile ; there  a huge  mass 
was  scored  through  at  the  top,  leaving  the  blocks 
standing  up  on  either  side  of  it,  as  if  castellated ; 
and  there  again  was  seen  a ponderous  lump,  so 
delicately  balanced  on  some  high  peak,  that  it 
seemed  as  if  the  least  gust  would  topple  it  over 
into  the  sea  beneath ; while  the  outline  of  the 
whole  was  as  jagged  as  if  it  had  been  gnawed,  or 
as  if  the  entire  granite  pile  were  some  immense 
crystal  that  the  sea  was  gradually  dissolving  away. 
Below  the  height  the  crags  stretched  far  out  into 
the  sea,  their  black  and  bluff  heads  peeping  up 
at  different  distances  through  the  waves  which 
compassed  them  with  a ring  of  the  whitest  foam ; 
while  at  the  end  of  the  winding,  broken  line,  there 
rose  one  rock  higher  than  the  rest,  and  on  top  of 
this  glistened  the  silver  tower  of  the  light-house, 
that,  like  a star-tipped  wand,  pointed  the  way. 


42 


THE  WONDERS  OF  SCIENCE. 


as  it  gave  the  first  glimpse  of  home  to  the  return- 
ing mariner.*  Far  beyond  this,  again,  the  eye 
could  just  trace,  in  the  mist  of  the  distance,  the 
cloud-like  islands!  studding  the  crystal  ring  of  the 
horizon,  while  all  the  rest  was  one  wide  desert  of 
water  stretching  away  to  the  Western  World,  that 
even  the  fancy  was  weary- winged  in  its  struggle  to 
reach. 

Nor  was  the  scene  behind  the  narrow  tongue  of 
land  that  forms  the  very  end  of  our  island  less  grand 
and  solemn  than  that  which  lay  before  it.  To  the 
southward  the  pathway  was  along  the  edge  of  a 
precipice  that  the  sea  beneath  had  scooped  into  a 
curve,  and  here,  at  one  extremity,  the  ocean  had 
drilled  huge  caldron-like  cavities  in  the  rock,!  and 
pouring  into  these  boiled  with  a roar  that  made  the 
cliffs  boom  again  with  the  noise.  Beyond  this  rose 
the  majestic  headland  of  “ Carn-y-Voel ,”  its  sum- 
mit half  veiled  by  a light  scarf  of  clouds,  and  its 
tall  sides,  built  of  granite  cubes,  rising  straight  as  a 
fortress  wall  from  out  the  sea.  Here  the  ocean 
had  worked  for  itself  a little  bav,  where  the  smooth 
green  water  lay  like  a mirror,  with  the  shadows  of 
the  yellowish-red  cliffs  above  it  reflected  deep  into 

* These  are  called  the  “ Long  Ships’  Rocks,”  and  on  one  ol 
them  is  a “light.”  British  ships  passing  this  pay  one  halfpenny 
a ton,  and  foreigners  one  shilling  each  vessel ; the  annual  reve- 
nue thus  obtained  amounting  to  three  thousand  pounds. 

| The  Scilly  Isles. 

t Known  by  the  name  of  “ Enys  Dodnan 


young  Humphry’s  resolves.  43 

the  pool,  and  trembling,  as  the  surface  rippled,  into 
zig-zag  lines  that  played  with  a thousand  lights  and 
shades.  On  the  other  side  of  this  bay  a low  granite 
cliff  jutted  out  like  a buttress,  the  green  ground 
above  sloping  abruptly  down  ; and  against  this  the 
waves  beat  and  dashed  till  the  spray  played  around 
the  rocks  like  a cloud  of  smoke,  and  sparkled  in  the 
sun  delicately  tinted  with  many  a prismatic  hue. 
Here,  again,  the  ocean  had  burrowed  into  the  thick 
granite  wall,  while  near  the  verge  of  the  cliff  there 
was  a perpendicular  shaft,  the  sides  of  which  were 
Smooth  and  circular,  as  if  they  had  been  drilled 
out  of  the  solid  rock  ; and  looking  down  these,  as 
down  a dark  well,  the  eye  could  see  the  white 
waves  tumbling  and  tossing  below  with  a terrible 
fury.* 

On  the  northern  side  of  the  promontory,  called  in 
Cornish  “ Antyer  Dewetli ,”  or  the  Land’s  End,  the 
headlands  were  higher  than  those  even  on  the  south, 
for  there  one  tall  rock  rose  out  of  the  waves  tower- 
ing high  into  the  air,  and  formed  also  of  granite 
cubes,  which  looked  in  the  distance  so  like  a suit  of 
mail,  that  it  had  acquired  the  name  of  the  “ Armed 
Knight and  here  at  the  very  top  of  one  of  the 
craggy  summits  a singular  cross  of  rock  was  to  be 
seen,  while  as  the  eye  travelled  along  the  curved 
and  crumpled  shore,  far  away  to  the  north,  it  rested 

* This. is  called  in  Cornish  “ Tol-Pedn-PenwithP  which  sig- 
nifies the  holed  headland  on  the  left  hand 


44 


THE  WONDEES  OF  SCIENCE. 


on  the  point  of  land  known  by  the  name  of  “ Cape 
Cornwall,”  the  outlines  and  tints  of  whose  slate 
cliffs,  seen  through  the  atmospheric  veil,  appeared 
soft  and  blue  with  the  haze  of  distance* 

Despite  the  blocks  of  granite  that  protruded 
through  the  land,  like  the  bones  of  the  earth  itself, 
the  ground  roundabout  was  rich  in  parts  with  flow- 
ers. Now  the  soil  was  purple  with  the  richest 
heaths,  and  now  it  was  yellow  as  a plate  of  gold 
with  the  bloom  of  the  dwarf-furze,  the  latter  filling 
the  air  with  a perfume  like  apricots,  while  the 
green  patches  of  grass  were  almost  iridescent  with 
the  various  wild  flowers  that  peeped  with  their  deli- 
cate blossoms  from  out  the  blades.  The  air,  too, 
was  savoury  with  the  odour  of  the  sea,  and  fresh 
with  the  spray  that,  like  a dew,  brushed  against  the 
cheek.  Still  amidst  the  solemn  convulsion  of  rocks 
and  the  vast  belt  of  water  which  encompassed  the 
beholder  as  far  as  the  sight  could  stretch,  a feeling 
of  overpowering  loneliness — a sense  of  one’s  own  in- 
significance and  helplessness,  such  as  travellers  are 
said  to  feel  in  deserts — oppressed  the  mind  there — 
there , at  the  very  brink,  as  it  were,  of  one’s  native 
country — the  last  bit  of  the  land  with  which  all 
one’s  affections  and  associations  were  linked — and 
rapt  in  a ghastly  silence,  that  was  broken  only  by 
the  moan-like  booming  of  the  monster  sea,  as  it  beat 
into  the  cavities  of  the  cliflf  far  beneath  the  feet,  or, 
now  and  then,  by  the  shrill  shrieking  of  the  cor' 


YOUNG  HUMPHRY’S  RESOLVES.  45 

morant,  or  the  whirr  of  some  passing  sea-mew’s 
wing.* 

The  boy  sat,  as  we  said,  for  a while  staring  va- 
cantly at  the  waves  that  pranced,  like  curvetting 
steeds,  before  him,  and  as  he  did  so  a heavy  tear- 
drop fell  now  and  then  on  the  moss  that  spotted  the 
rock  at  his  feet.  Sometimes  his  lips  would  move, 
though  not  a word  escaped  them,  and  he  would 

* Davy  is  said  to  have  delighted  as  a boy  in  visiting  the  Land’s 
End.  In  one  of  his  early  poems  occurs  the  following  passage,  in 
which  the  spot  is  spoken  of  under  its  Latin  name,  “Bolerium 

“ Thy  awful  height,  Bolerium,  is  not  loved 
By  busy  man  ; and  no  one  wanders  there 
Save  he  who  follows  Nature — he  who  seeks 
Amidst  thy  crags  and  storm-beat  rocks  to  find 
The  marks  of  changes,  teaching  the  great  laws 
That  raised  the  globe  from  chaos  ; or  he  whose  soul 
Is  warm  with  fire  poetic.” 

“ It  is  surely  not  difficult,”  says  Dr.  Paris,  “to  understand  how 
it  happened  that  a mind  endowed  with  the  genius  and  sensi- 
bility of  Davy  should  have  been  directed  to  the  study  of  chemis- 
try and  mineralogy,  when  we  consider  the  nature  and  scenery  of 

the  country  in  which  accident  had  placed  him Nor  could 

he  have  wandered  along  the  rocky  coast,  nor  have  reposed  for  a 
moment  to  contemplate  its  wild  scenery,  without  being  invited 

to  geological  inquiry ‘ How  often,  when  a boy,’  said 

Davy  to  me  (adds  the  Doctor),  on  my  showing  him  a drawing  of 
the  wild  rock  scenery  of  Botallack  Mine,  ‘have  I wandered  about 
those  rocks  in  search  of  new  minerals,  and,  when  fatigued,  sat 
down  upon  the  turf,  and  exercised  my  fancy  in  anticipation  of 
scientific  renown.’”  (Botallack  Mine  is  situate  at  St.  Just,  a 
town  near  to  Cape  Cornwall,  and  but  a short  distance  from  the 
Land’s  End.)  “The  granite  and  serpentine  rocks  of  his  native 
county  were,  I believe,”  says  Dr.  John  Davy,  “the  first  he 
studied  when  he  commenced  the  pursuit  of  geology,  and  both  of 
them  were  to  him  particularly  attractive.  The  finest  examples  of 


i 


46 


THE  WONDERS  OF  SCIENCE. 


strike  the  air  with  his  clenched  fist  as  though  a 
sudden  resolution  had  crossed  his  mind ; then  a 
shudder  would  pass  over  his  frame,  and  he  would 
clasp  his  forehead  with  both  his  hands,  and  sway 
his  body  to  and  fro,  as  he  bent  his  head  almost  to 
his  knees.  Presently,  after  a slight  pause,  he  would 
raise  his  head,  and  with  his  neck  stretched  back, 
look  steadfastly  at  the  heavens  as  if  gazing  at  some 
spirit  there.  And  when  this  fit  was  passed,  he 

these  rocks  were  within  a day’s  ride  of  Penzance  ; and  -when  he 
visited  home,  a young  man,  he  never  failed  paying  the  Lizard  and 
the  Land’s  End  a visit,  and  generally  in  company  with  some  of 
his  old  school-fellows.  I remember,’ when  a boy,”  Dr.  D.  con- 
tinues, “ being  allowed  to  join  one  of  these  parties  to  the  Land’s 
End,  and  it  was  a merry  one — as  youthful  parties  commonly  are. 
After  exploring  the  cliff  scenery,  we  dined  at  a tavern  at  St.  Just, 
and  I well  recollect  the  boisterous  mirth  indulged  in  when  the 
repast  was  concluded — the  gymnastic  feats  attempted,  the  shouts 
of  applause,  the  unconstrained  laughter,  and  all  that  abandonment 
of  spirit  to  mirth  so  common  to  young  persons  under  excitement, 
and  which,  excepting  in  jmuth,  can  scarcely  be  felt  or  enjoyed.” — 
Life  of  Sir  Humphry  Davy. 

In  the  commencement  of  a work  designed  by  Sir  Humphry 
Davy  upon  “ The  Geology  of  Cornwall,”  the  philosopher  himself 
gives  the  following  description  of  the  rocks  at  the  Land’s  End  : 
“ In  the  great  arrangement  of  the  masses  of  granite  of  Cornwall, 
the  rock  appears  composed  of  an  immense  number  of  blocks  of 
different,  sizes.  This  structure  is  nowhere  more  perfectly  ex- 
hibited than  in  the  western  cliffs.  The  incessant  agency  of  the 
Atlantic,  its  storms  and  its  waves,  have  washed  away  or  destroyed 
all  the  loose  materials  of  the  shore,  and  left  abrupt  eminences  of 
rock  from  50  to  360  feet  in  height.  The  arrangement  of  the  grand  e 
is  in  masses  which  approach  to  the  cubical  form,  having,  how- 
ever, rounded  edges,  heaped  upon  each  other.  . . . The  masses 
are  grand,  their  colours  uniform,  and  their  uniformity  increases 
the  effect  upon  the  eye  ; while  the  arrangements  of  this  kind  have 


YOUNG  HUMPHRY’S  RESOLVES.  47 

would  resume  liis  seat,  and  clasp  his  hands  as  in 
prayer. 

Suddenly  the  boy  started  to  his  feet,  crying, 
“Yes,  I’ll  do  it — that  I will.  I will  rescue  them 
all  — every  one  — from  the  poverty  that  threatens 
them.  I have  promised  my  dead  father  to  do  so. 
I have  prayed  God  to  give  me  the  strength  and 
firmness  to  carry  out  my  purpose,  and  in  a few  years 
our  home  shall  be  as  happy  as  it’s  wretched  now. 

a peculiar  wildness  and  sublimity.  Nowhere  is  it  seen  upon  a 
greater  scale,  or  in  a more  magnificent  assemblage  of  forms,  than 
from  a point  between  the  Land’s  End  and  Castle  Treene.  Both 
these  grand  promontories  appear  extending  into  the  Atlantic ; 
the  cliffs  between  them  are  abrupt  and  lofty  ; the  waves  are 
broken  by  a number  of  small  island  rocks,  which  are  scattered 
along  the  shore.  The  few  portions  of  soil  that  appear  above  the 
cliff  are  covered  with  short  green  grass,  tufted  with  heath  and 
furze,  which,  in  the  autumn,  present  mixed  hues  of  purple  and 
gold.  The  rock  throughout  is  of  a uniform  yellowish  red,  the 
tint  perfectly  contrasted  to  the  blue-greens  of  the  sea.”  (Castle 
Treene,  or  “ Castle  Treryn,”  as  it  is  more  correctly  written,  is 
a headland  beyond  “ St.  Levan  churchtown,”  as  it  is  sometimes 
called — though  the  chapel  which  formerly  stood  there  has  been 
many  years  since  washed  away  b}r  the  sea,  the  steps  alone  now 
remaining.)  St.  Levan  lies  a little  to  the  eastward  of  the  head- 
land called  “ Tol  Pedn  Penwith .”  A short  distance  from  St’ 
Levan  is  “ Port  Carnow  Cove,”  which  is  bounded  on  the  eastern 
side  by  rocks  that  jut  far  into  the  waves,  and  rise  to  a great 
height,  being  heaped  one  on  another,  in  magnificent  order.  Here 
stands  the  noble  headland  called  “ Castle  Treryn,”  above  whose 
summit  two  huge  slanting  and  imposing  masses  of  granite  pro- 
trude. There  is  a fissure  between  these  masses  leading  to  a 
smaller  group  of  granite  rocks,  on  the  top  of  which  the  huge 
Logan  stone  (weighing  some  65  tons)  stands  so  delicately  poised, 
that  by  clambering  to  a fearful  height  at  one  of  the  angles,  it  may 
be  made  to  sway  to  and  fro  with  the  least  force. 


48 


THE  WONDERS  OF  SCIENCE. 


I feel  as  if  I had  just  woke  from  a long  dream.  What 
a thoughtless,  idle  fool,  I’ve  been!  but  it’s  past — 
never  to  return.  Poor  mother  ! I’ve  cost  her  many 
a tear,  I know,  of  late.  Plow  have  I wasted  this 
last  year,  when  I should  have  been  at  some  business 
seeking  the  means  of  adding  to  my  mother’s  com- 
forts, instead  of  lessening  the  little  that  is  left  her  at 
such  a time  as  this ! If  I had  only  worked  instead 
of  squandering  my  time  in  silly  pleasures,  I might 
now  have  been  a help  to  her  rather  than  the  wretch- 
ed burden  I am — without  the  power  to  earn  a crust 
for  myself.  What  do  I know  that  is  of  use  to  any 
one?  "Who  would  give  me  a penny  for  anything 
that  I can  do  ? and  yet  I’m  old  and  strong  enough  to 
get  my  own  living.  Oh,  shame  ! shame  ! that  I,  at 
my  time  of  life,  should  have  to  take  from  poor  moth- 
er’s little  store.  If  I’d  had  a proper  spirit,  I should 
have  felt  this  long  ago : but  no  matter,  it’s  ended 
now ; and  I’ll  go  to  work  and  so  fill  my  mind  with 
knowledge  that  mother  shall  soon  be  as  pleased  about 
me,  as  I know,  poor  thing ! she  has  been  pained  of 
late.  Yes,  and  father  will  watch  over  me  ; I know 
he  will.  Oh  ! if  I could  only  have  changed  before  he 
died,  what  a comfort  it  would  have  been  to  him  in 
his  last  moments : but  as  it  was,  I,  like  a wretch, 
let  him  leave  me  in  doubt  as  to  what  was  to  become 
of  me.  Why  didn’t  I wake  up  before  ? If  it  had 
only  been  a month  ago,  he  might  have  felt  no  pain 
on  my  account.  Oh,  shame ! shame ! but,  thank 


young  Humphry’s  resolves. 


49 


God,  I’m  different  now,  and  I’ll  go  back  home  and 
tell  mother  all  I mean  to  do.  I’ve  the  power  in  me 
— I know  I have.  I’ll  go  back  and  tell  her  not  to 
grieve,  and  that  I’ll  do  all  I can  to  help  her  and  my 
brother  and  sisters  for  the  future.”* 

* Dr.  John  Davy  says,  “ The  greater  part  of  the  year  follow- 
ing” (the  period  of  his  quitting  Dr.  Cardew’s  school  at  Truro, 
which  Humphry  did  at  the  age  of  fifteen,  when  his  school  edu- 
cation was  considered  as  complete)  “he  was,  I believe,  in  an 
unsettled  state,  stud3ung  in  a desultory  manner,  by  fits  and 
starts,  and  3'ielding  to  the  allurements  of  occasional  dissipation, 
and  the  amusements  which  constitute  the  delight  of  active  youth 
— as  fishing,  shooting,  swimming,  and  solitary  rambles.  This 
was  -perhaps  the  most  dangerous  period  of  his  life,  and  in  conversation 
with  me  he  has  so  spoken  of  it.  Amusement  threatened  for  a time 
to  obtain  the  mastery,  and  keep  him  down  to  the  common  level ; 
but  his  good  genius  triumphed,  and,  after  a few  months’  vacilla- 
tion, he  applied  himself  in  earnest  to  the  cultivation  of  his  mind 
and  to  the  acquisition  of  knowledge  ; and  the  flame  once  kindled 
burnt  on  till  it  expired  in  death.”  Speaking  of  the  circumstances 
which  induced  Humphry  to  relinquish  all  his  boyish  habits  about 
the  period  of  his  father’s  death,  his  brother  says  : “ This  event , 
probably,  had  a powerful  effect  in  giving  steadfastness  to  his  resolu- 
tion, and  I am  quite  certain  that  the  circumstances  of  his  family  be- 
came with  him  an  additional  and  powerful  motive  to  exertion .” 

“ Like  most  young  persons,  Humphry  when  a boy,”  says  Dr. 
John  Davy,  “was  fond  of  declaiming,  and  indulged  in  it  in  his 
solitary  walks  and  rambles.  On  one  occasion  it  is  recorded  of 
him,  that,  on  his  way  to  visit  a poor  patient  in  the  country” 
(during  his  apprenticeship),  “ in  the  fervour  of  declamation,  he 
threw  out  of  his  hand  a phial  of  medicine  which  he  had  to  admin- 
ister, and  that  when  he  arrived  at  the  bed-side  of  the  poor  woman 
he  was  surprised  at  the  loss  of  it.  The  potion  was  found  the 
next  day  in  a hay-field  adjoining  the  path”  (p.  55). 

D 


CHAPTER  HI. 


HUMPHRY  AND  HIS  MOTHER. 

The  resolution  once  formed,  young  Humphry 
hastened  to  convey  the  glad  tidings  to  his  mother, 
and  as  he  rode  along  he  kept  talking  to  himself  all 
the  way,  running  over  the  many  “fine  things”  he 
meant  to  do  for  the  future,  and  dreaming  that  some 
day  he  might  perhaps  become  distinguished  for  his 
learning  and  wisdom.  He  amused  himself,  too,  by 
speculating  as  to  what  he  would  do  with  his  money 
if  he  ever  got  to  be  rich.  He  would  have  his  little 
brother  John  well  educated  then,  and  comfortably 
started  in  life.  Yes ! and  he  would  give  up  his  share 
in  the  property  at  Varfell  to  his  mother  and  sisters — 
it hat  he  would  do  first  of  all ; and  if  he  grew  to  be  a 
very  wealthy  man,  he  would  give  a certain  sum  of 
money  to  the  Grammar-school,  so  that  the  boys 
might  have  a holiday  every  year  on  his  birthday — - 
he  would  like  to  be  able  to  do  that,  for  then  he 
would  be  remembered  by  them  as  long  as  the  school 
lasted.  Further,  he  would  give  something  a year 
to  his  aunt  Sampson’s  Phillis,  and  his  aunt  Millett’s 
maid  as  well.  Poor  Mary  Launder  and  Betty 


HUMPHRY  AND  HIS  MOTHER. 


51 


White  should  get  something,  too ; and  he  would 
have  a number  of  old  pensioners  besides,  that  had 
known  him  when  he  was  young.  He  would  take 
care,  moreover,  that  his  pony  Derby  and  his  dog 
Cliloe  wanted  for  nothing  in  their  old  age,  and 
wherever  he  might  be  he  would  have  a box  of 
apples  sent  him  at  Christmas  from  the  tree  he 
had  planted  in  the  garden  when  he  was  a little  fel- 
low. * 

On  reaching  the  humble  farm  at  Varfell,  Hum- 

* The  greater  number  of  these  resolves  were  fulfilled  in  after- 
life. Dr.  John  Davy  says  : “ The  interest  he  took  in  me  more 
resembled  that  of  a father  than  a brother,  and  it  is  with  peculiar 
pleasure  I reflect  on  his  various  kindnesses — my  numerous  obli- 
gations, many  of  which  were  delicately  concealed  at  the  time — 
his  valuable  hints  and  generous  regard  to  my  studies,  leaving 
me  free  to  follow  the  bias  of  my  own  mind — and  his  excellent 
advice  in  respect  to  my  conduct,  in  which  was  always  infused 
a native  nobleness  of  sentiment  well  adapted  to  stir  up  virtue  in 
a young  mind.”  In  one  of  his  letters  to  his  brother,  Sir  Hum- 
phry says,  “You  must  study  your  own  plans  with  respect  to 
study.  Pray  do  not  care  about  the  expense,  if  it  adds  anything 
to  the  comfort  or  respectability  of  your  situation.  I will,  if  you 
like,  send  L40  a year,  in  addition  to  what  my  mother  sends  you. 
My  dear  John,  let  no  difficulties  alarm  you;  you  may  be  what 
you  please.  Let  no  example  induce  you  to  violate  decorum — 
no  ridicule  prevent  you  from  guarding  against  sensuality  or  vice. 
Live  in  such  a way  that  you  can  always  say  the  whole  world  may 
know  what  I am  doing.” 

Dr.  Paris  says  : “ No  sooner  had  Davy  found  himself  in  a 
situation  which  secured  for  him  the  necessaries  of  life,  than  he  re- 
nounced all  claims  upon  his  paternal  property  in  favour  of  his  mother 
and  sisters .”  In  a letter  to  one  of  his  sisters,  Davy  says  r “ I 
enclose  a one-pound  note,  which  you  will  lay  out  in  books  or  in 
anything  else  you  like.  I enclose  another  one-pound  note,  which 
I wish  to  have  disposed  of  in  the  following  manner:  To  Mary 


52 


THE  WONDERS  OF  SCIENCE. 


phry  found  his  mother  seated  beside  a table,  the 
top  of  which  was  black  with  a hillock  of  little 
skirts  and  bodies  that  she  had  been  busy  making 
up  for  the  children’s  week-day  wear.  The  quick 
eye  of  the  boy  could  distinguish  as  he  glanced  at  the 
pile  of  mourning  that  the  gloss  of  the  bombazeen 
was  dulled  in  places  with  the  tears  that  had  fallen 
upon  it. 

Humphry,  from  a sense  of  the  grief  that  pervad- 
ed the  house,  had  entered  the  room  so  softly  that 


Launder,  5s. ; to  Betty  White,  5s. ; and  with  the  rest  you  will 
buy  some  ribbons  or  little  articles  of  dress  for  the  Doctor’s  Jen- 
ny, my  aunt  Sampson’s  Phillis,  my  aunt  Millett’s  maid,  and  my 
mother’s  servant,  as  New-years’s  gifts.”  In  another  letter  he 
writes  thus  : “ I enclose  a ten-pound  note,  which  I beg  you  will 
lay  out  in  the  way  3mu  think  best  for  my  sister’s  children  and  any 
old  pensioners  that  knew  me  in  my  youth.”  “ No  Swiss  peasant,” 
says  Dr.  Paris,  “ ever  sighed  more  deeply  for  his  native  mount- 
ains than  did  Davy  for  the  scenes  of  his  early  years.  He  entreat- 
ed his  nurse  (when  ill  at  the  Royal  Institution)  to  convey  to  his 
friends  his  ardent  w'ish  to  obtain  some  apples  from  a particular 
tree  which  he  had  planted  when  a boy,  and  he  remained  in  a state 
of  restlessness  and  impatience  until  their  arrival.”  Moreover,  it 
should  be  stated,  that,  in  addition  to  his  will,  he  left  at  his  death  a 
paper  of  directions,  which  have  been  religiously  observed  by  his 
widow.  In  these  he  desires  that  the  interest  arising  from  £100 
stock  may  be  annually  paid  to  the  master  of  the  Penzance  Gram- 
mar-school, on  condition  that  the  boys  may  have  a holiday  on  his 
birthday.  “ There  is  something,”  adds  Dr.  Paris,  “ singularly 
interesting  in  this  favourable  recollection  of  his  native  town  and 
of  the  associations  of  his  early  youth.  It  adds  one  more  example 
to  show,  that,  whatever  may  have  been  our  destinies,  and  how- 
ever fortune  may  have  changed  our  condition,  where  the  heart 
remains  uncorrupted  we  shall,  as  the  world  closes  upon  us,  fix 
our  imaginations  upon  the  simplicities  of  our  youth,  and  be 
cheered  and  warmed  by  the  remembrance  of  early  pleasures.”  - 


HUMPHRY  AND  HIS  MOTHER, 


53 


his  presence  was  unperceived  by  the  widow,  and 
for  a minute  or  two  he  stood  watching  his  mother 
as  she  sat  there  with  her  flooded  eyes  fixed  intently 
on  the  large  carved  oak-chair  (her  late  husband’s 
handiwork)  that  stood  beside  the  mantel-piece.  Her 
cheek  rested  on  her  hand,  and  it  was  plain  by  the 
fixedness  of  her  gaze  that  the  seat  was  no  longer 
empty  to  her,  and  that  her  mind  was  far  away  in 
the  past. 

The  sight  of  that  sad  wife,  widowed  almost  in  her 
youth,  was  sufficient  to  have  touched  many  a stout- 
er heart  than  young  Humphry’s.  The  widow’s 
hair  was  still  un silvered  by  age,  and  its  blackness 
contrasted  forcibly,  and  even  painfully,  with  the  close 
white  muslin  cap  that  half  concealed  it.  The  dead 
black  of  the  crape  made  her  cheek  as  pale  as  marble, 
while  the  tears  that  dewed  her  eyes  gave  them  an 
almost  glassy  look,  so  that  they  seemed  jettier  than 
usual.  Her  face,  though  young  in  years,  was  pre- 
maturely old  in  expression,  for  the  features,  which 
were  naturally  well  formed,  were  pinched ; and  there 
was  an  air  of  mild  resignation  over  the  countenance 
that  told  you  the  poor  woman  had  long  ago  learnt 
to  bear  affliction,  almost  without  complaint.  Nor 
did  it  need  a second  glance  to  discern  the  tender- 
ness and  affection  of  her  nature* — for  though  there 

* “ In  all  the  various  situations  of  life  in  which  my  mother  was 
placed,”  says  Dr.  John  Davy,  “she  so  conducted  herself  as  to 
gain  the  regard  and  good-will  of  every  one.  She  possessed  a 
most  kind  and  affectionate  heart,  a pious  mind,  sound  under- 
standing, and  perfect  integrity.  She  was  devoted  to  the  per- 


54 


THE  WONDERS  OF  SCIENCE. 


was  a settled  melancholy  in  her  face,  there  was  still 
so  much  kindliness  in  its  expression  that  the  heart 
could  not  help  extending  to  her  the  sympathy  that 
it  knew  she  would  be  the  first  to  afford  to  others 
who  had  seen  as  much  trouble  as  she  herself  had  in 
the  course  of  the  few  years  that  had  passed  over  her 
head. 

Humphry  drew  towards  his  mother’s  chair,  and 
resting  against  the  back  curled  his  arm  gently  about 
her  neck.  So  unexpected,  however,  was  the  em- 
brace, that  the  widow  shrieked  with  alarm  as  she 
was  suddenly  roused  from  her  melancholy  reverie. 

The  next  moment,  pleased  at  the  idleness  of  her 
fright,  she  clasped  the  pet  boy  to  her  ; and  while  the 
tears  gushed  from  her  eyes  she  kissed  him  again  and 
again,  as  though  she  loved  him  the  more  now  that 
he  and  her  other  children  were  all  that  she  had  left 
to  engross  her  affection. 

“What!  in  tears  again,  mother1?”  said  Hum- 
phry, in  a tone  of  kindly  remonstrance.  “ Nay,  do 

formance  of  all  her  duties,  and  was  remarkably  free  from  all  guile 
and  foolish  pride.  When  she  became  a widow,  she  was  in  her 
thirty-fourth  year,  wuth  five  children,  all  of  whom  were  still  to  be 
educated,  excepting  Humphry,  her  eldest  son.  Her  income  at 
this  time  was  about  =£150  a-year,  and  it  w as  encumbered  with  a 
debt  of  about  ,£1300,  contracted  by  my  father  chiefly  in  conse- 
quence of  losing  speculations  in  mining.  Her  good  resolutions 
did  not  fail  her  on  this  trying  occasion  ; she  met  all  her  difficul- 
ties with  courage  and  prudence.” 

Dr.  Paris,  speaking  of  Davy  ’s  mother,  says  : “ She  was  re- 
markable for  the  placidity  of  her  temper  and  for  the  amiable  and 
benevolent  tendency  of  her  disposition.” 


HUMPHRY  AND  HIS  MOTHER. 


55 


not  grieve,”  he  added,  as  the  widow  rested  her  head 
on  his  bosom,  “ I have  come  to  promise  you  that 
I will  do  all  in  my  power  for  my  brother  and 
sisters.”* 

“ But  what  can  you  do,  Humphry,  my  good  lad  ?” 
asked  the  mother,  as  she  looked  up  through  her 
tears  and  smiled  at  the  youth.  “ It  will  take  you 
some  years  before  you  can  earn  a livelihood,  and  even 
then  perhaps  you  will  gain  only  sufficient  for  your 
own  wants.  What  is  to  become  of  my  little  ones  is 
more  than  I can  bear  to  think  of.  How  you,  too, 
Humphry,  are  to  be  put  out  in  the  world,  I’m  sure 
I cannot  say.  My  means,  when  all  the  debts  are 
paid,  will  be  only  £100  a-year,  if  that.” 

“ There,  there ; have  no  trouble  on  my  account, 
mother,”  returned  the  lad.  “ I’ve  made  up  my  mind 
to  lay  aside  all  my  idle  habits,  and  to  set  hard  to 
work  at  something  directly — though  I cannot  tell 
what,  just  now ; and  you  shall  see  I won’t  be  long 
before  I make  you  all  happy  here.” 

The  mother  half  laughed  at  the  sanguineness  of 
her  son,  and  said,  when  she  had  kissed  him  for  his 
kindness,  (‘But  you  talk  like  a boy,  Humphry. 
You  don’t  know  how  hard  it  is  to  earn  money  yet.” 

“ Yes  I do , mother,”  replied  the  determined  youth, 

* “ My  brother,”  says  Dr.  John  Davy,  “ at  the  time  of  my 
father’s  death  was  sixteen  years  old.  Seeing  her  (Mrs.  Davy) 
in  great  affliction,  he,  in  a very  affectionate  manner,  begged  her 
‘not  to  grieve,’  saying  that  ‘he  would  do  all  he  could  for  his 
brother  aud  sisters'  ” 


56 


THE  WONDERS  OF  SCIENCE. 


as  he  pressed  her  hand.  “But  I feel  I have  the 
power  in  me,  and  I’ll  do  it,  you  shall  see — all  by 
myself  too — aye,  that  I will,  if  I have  to  study 
night  and  day.  You  don’t  know  what  a lesson 
noor  father’s  death  has  been  to  me.  I never  saw 

x 

you  in  grief  before,  and  all  this  last  week  my  mind 
has  been  at  work,  for  your  tears  were  more  than  I 
could  bear.  Not  a night  of  late  has  past  but  I 
have  reproached  myself  over  and  over  again  that 
I had  wasted  the  last  year  of  my  life,  instead  of 
doing  something  that  would  have  given  me  the 
power  to  help  you  at  such  a time  as  this.  When 
I heard  Mr.  Tonkin,  too,  talking  with  you  the  other 
day  about  the  money  you  would  have  to  live  upon, 
and  heard  him  say  that  it  was  high  time  I should 
cease  being  a burden  to  you — yes,  those  were  his 
words,  mother — a harden ” (and  the  boy  would  have 
turned  away  from  the  widow,  but  she  held  his 
hand),  “I  felt  the  blood  rush  into  my  face  with 
shame,  and  a new  spirit  came  over  me.  I didn’t 
say  anything  to  you,  mother,  at  the  time,  because  I 
thought  I could  hardly  trust  myself ; but  I went  on 
thinking  I teas  a burden  to  you,  and  the  heaviest 
burden  of  all,  too.  So  I kept  brooding  and  brood- 
ing it  over,  until  at  last  I made  a solemn  determ- 
ination that,  instead  of  a burden,  I would  be  a 
help  to  you  and  my  brother  and  sisters  for  the 
future.  I have  sworn  it,  mother ! I have  prom- 
ised my  poor  father  to  do  so  this  very  day — alone 


HUMPHRY  AND  HIS  MOTHER. 


57 


among  the  rocks  I made  the  vow,  and  I’m  sure  he 
heard  me,  for  I feel  as  I never  felt  before,  and  I 
know  I’ve  the  power  to  do  as  I have  said.” 

The  mother  in  her  delight  hugged  the  boy  pas- 
sionately to  her  bosom,  and  as  her  tears  fell  thick 
and  hot  upon  him  she  said  through  her  sobs,  “You 
have  the  power,  I know,  Humphry ; and  if  this  sad 
bereavement  which  has  come  upon  us  all  does  but 
stir  you  to  make  use  of  the  genius  that  is  in  you, 
it  will  be  indeed  almost  a recompense  for  the  heavy 
loss  we  have  sustained.  When  you  were  but  a 
child,  I used  to  tell  your  dear  father  of  the  bright 
hopes  I had  of  you,  Humphry,  and  that  I was  sure 
you  would  be  very  clever  some  day  ; though  he,  poor 
man ! only  smiled  at  my  words,  and  thought  it  was 
my  over-fondness  that  made  me  fancy  as  much,  say- 
ing all  mothers  did  the  same.  But  I knew  different- 
ly, Humphry ; I could  see  you  were  not  like  other 
children,  and  even  from  an  infant  there  was  hardly 
anything  babyish  about  you.  When  you  were  only 
five  years  old  you  made  rhymes  of  your  own,  and 
used  to  recite  them  in  the  Christmas  gambols,  and  I 
knew  there  was  no  little  thing  of  that  age  that  could 
do  the  same  thing  in  these  parts.” 

“Yes,  I’ve  often  heard  you  say  so,  mother,” 
added  the  boy,  smiling  at  the  youthful  reminis- - 
cence. 

“ You  were  a very  forward  child — from  a baby  I 
may  say,  Humphry,”  continued  the  proud  mother, 


THE  WONDERS  OF  SCIENCE. 


5« 

as  she  passed  her  fingers  through  the  lad’s  hair,  and 
brushed  it  from  his  forehead — for  she  half  forgot 
her  sorrow  as  the  recollection  of  her  pet  boy’s  feats 
stole,  one  after  another,  across  her  mind.  44  Why, 
you  were  only  nine  months  old  when  you  walked 
off,  all  by  yourself ; and  you  could  speak  as  well, 
and  fluently,  as  a little  man,  before  you  were  two 
years  of  age.  Shall  I tell  you,  too,  what  you  said 
when  your  sister  Kitty  was  born  ? little  sharp  thing 
as  you  were ! The  servant  had  been  assuring  you 
day  after  day,  that  when  the  baby  came  you’d  be  no 
longer  petted  in  the  way  you  had  been — for  then,  as 
the  maid  said.  4 your  nose  would  be  put  out  of  joint.’ 
This  seemed  to  make  a great  impression  upon  you, 
for  directly  you  saw  little  Kitty  you  put  your  chub- 
by fat  hand  up  to  your  face,  and  cried,  4 Mamma! 
my  nose  not  out  of  joint  at  all.’  ” 

44  Did  I ?”  laughed  Humphry. 

44  Yes,  that  you  did,”  said  the  mother.  44  Ay, 
and  before  you  had  learned  to  write  you  used  to 
copy  the  figures  in  4 .iEsop’s  Fables,’  and  print  the 
names  of  them  in  big  letters  underneath.  I really 
think,  too,  you  couldn’t  have  been  more  than  four 
years  old  when  you  could  recite  a good  part  of 
‘Pilgrim’s  Progress.’  All  I know  is,  you  did  so 
before  you  could  read  well  the  book;  for  your 
memory  was  so  great,  that  anything  you  had  heard 
once  or  twice  you  could  repeat,  almost  without  a 
mistake,  afterwards ; and  when  you  were  sent  to 


HUMPHRY  AND  HIS  MOTPIER. 


59 


Mr.  Bushel? s school — you  remember  old  Mr.  Bush- 
ell,  Humphry — you  made  such  rapid  progress  there 
in  your  reading  and  writing,  that  though  you  were 
only  six  years  of  age,  the  old  gentleman,  against  his 
own  interest,  recommended  your  poor  father  to  re- 
move you  to  the  Grammar-school.* 

* “It  is  remembered,”  says  Dr.  John  Davy,  speaking  of  Sir 
Humphry’s  infancy,  “ that  he  walked  off  (to  use  a nursery  phrase) 
when  he  was  just  nine  months  old ; and  I have  been  told,  that 
before  he  was  two  years  of  age  he  could  speak  fluently.  About 
this  time  my  eldest  sister  was  born,  and  he  was  told  by  a serv- 
ant, that  on  her  appearance  ‘his  nose  would  be  put  out  of  joint.’ 
On  seeing  the  baby,  it  is  related  of  him,  that  he  put  his  hand  to 
his  nose,  and  said,  ‘Mamma,  my  nose  not  out  of  joint.’  Be- 
fore he  had  learned  to  write,  he  amused  himself  with  copying 
the  figures  in  ‘AECsop’s  Fables,’  and  under  his  drawings,  in  great 
letters,  he  contrived  to  give  them  their  names.  His  memory  was 
very  retentive,  in  proof  of  which  it  is  handed  down  in  the  fam- 
ily, that  when  very  young  he  could  recite  a great  part  of  ‘ Pil- 
grim’s Progress,’  even  before  he  could  well  read  it.  I believe 
that,  like  Pope,  he  lisped  in  numbers.  I remember  hearing  my 
mother  say,  that  when  scarcely  five  years  old  he  made  rhymes, 
and  recited  them  in  the  Christmas  gambols.  His  disposition  as 

a child  was  remarkably  sweet  and  affectionate The  first 

school  he  was  sent  to  was  that  of  a Mr.  Bushell,  at  which  read- 
ing and  writing  only  were  taught.  This  master,  then  an  old  man, 
remarking  the  rapid  progress  of  his  young  pupil  (he  was  then 
six  years  old),  in  a very  disinterested  manner  recommended  my 
father  to  remove  him  to  the  Grammar-school.” 

“ It  is  a fact,”  says  Dr.  Paris,  “worthy,  perhaps,  of  being  re- 
corded, that  Humphry  Davy  would,  at  the  age  of  five  years,  turn 
over  the  pages  of  a book  as  rapidly  as  if  he  were  merely  engaged 
in  counting  the  leaves  or  in  hunting  after  pictures,  and  yet,  on 
being  questioned,  he  could  generally  give  a very  satisfactory  ac- 
count of  the  contents.  The  same  faculty  was  retained  by  him 
through  life.” 


60 


THE  WONDERS  OF  SCIENCE, 


“ When  you  could  read,  too,  I often  watched  you 
at  your  books,  and  saw  you  turn  over  the  pages  so 
fast,  that  I fancied  you  were  merely  counting  them, 
or  hunting  for  pictures  ; but  on  talking  to  you  about 
the  book  I used  to  find,  to  my  astonishment,  that  you 
had  read  it  through  in  that  short  time,  and  that  you 
really  knew  all  about  it,  and  could  give  a much  bet- 
ter account  of  it  than  children  who  might  have  taken 
hours,  or  perhaps  days,  to  get  through  it.” 

Humphry  drew  closer  to  his  mother,  and  pressed 
her  hand  between  his  palms  as  he  looked  up  in  her 
face,  and  smiled  with  delight  to  hear  her  run  over 
all  the  feats  of  his  youthful  genius;  for  with  the 
history  of  each  little  wonder  he  felt  the  faith  he  wish- 
ed to  have  in  his  own  powers  grow  stronger  in  him, 
and  he  shook  his  head  proudly  as  he  inwardly  thought 
of  the  greater  wonders  he  would  achieve  in  the  time 
to  come. 

“ Go  on,  mother,”  he  said,  as  he  seated  himself  on 
the  stool  at  the  widow’s  feet,  “ tell  me  some  more 
things  I used  to  do  when  I was  a little  fellow — tell 
me  some  more,  they  fill  me  with  the  same  hope  as 
you  say  they  did  you,  and  I want  to  have  all  the 
trust  I can  in  myself ; for  I’ve  made  up  my  mind  to 
be  a great  man,  and  if  I doubt  my  power  to  accom- 
plish the  task  I have  set  myself,  I shall,  perhaps,  give 
it  up  almost  at  the  first  difficulty.  Tell  me  some- 
thing more,  mother ; I want  all  the  faith  in  myself 
you  can  give.” 


HUMPHRY  AND  HIS  MOTHER. 


61 


“I  wish  I could  give  you  as  much  confidence  in 
your  own  powers,  Humphry,  as  I have  in  them,5’ 
returned  the  widow,  “though  now  you  begin  to 
speak  with  all  the  aspirations  I have  longed  to  see 
coming  upon  you;  and  for  the  last  year  I cannot 
tell  you  how  grieved  I have  been  to  behold  one,  of 
whom  I had  formed  such  high  hopes,  giving  him- 
self up  to  pleasures  that  serve  to  breed  only  habits 
of  thoughtless  amusement  rather  than  wise  reflec- 
tion.” 

“ I know  I have  pained  you,  mother,”  added  Hum- 
phry, “but  it’s  all  at  an  end  now.  You  remember 
when  I was  at  the  Grammar-school,  how  Mr.  Cory- 
ton  used  to  pull  my  ears  for  not  minding  the  lessons 
he  set  me.  But  do  you  know,  mother,  I have  often 
thought,  that  though  I learnt  little  at  Mr.  Coryton’s 
school,  it  was,  perhaps,  better  after  all  that  I should 
have  been  left  to  teach  myself;  for  what  we  learn 
from  our  own  liking,  we  seldom  forget ; and  I am 
sure  I remember  more  about  the  books  I have  had 
from  Mr.  Tonkin,  and  that  I used  to  read  through 
one  after  the  other  as  fast  as  I could  get  them,  than 
all  the  Latin  and  Greek  I was  forced  to  get  by  heart 
at  school.”* 

* “ The  Rev.  Mr.  Coryton  (the  master  of  the  Grammar-school) 
was  a man  of  irregular  habits,  and  ill-fitted  for  the  office  of  teach- 
ing youth.  He  was  occasionally  severe,  and  punished  heavily 
slight  offences.  Pulling  the  boys’  ears  was  practised  by  him  in 
the  most  capricious  manner,  and  my  brother  was  too  frequently 
a sufferer  from  this  infliction.  It  is  recorded  of  Humphry  Davy, 


62 


THE  WONDERS  OF  SCIENCE. 


“ Ah,  but  Mr.  Cory  ton,”  interrupted  the  mother, 
“ was  a man  little  fitted  for  teaching  youth,  Hum- 
phry. He  was  careless  about  the  boys’  studies, 
and  often  very  severe  for  the  slightest  faults.  I re- 
member once  you  went  to  school,  unknown  to  me, 
with  a large  plaster  on  each  ear,  and  when  Mr. 
Coryton  asked  you  ‘ what  was  the  matter  with  your 
ears,’  you  told  him  4 that  you  had  put  the  plasters  on 
to  prevent  a mortification.’  But  if  you  didn’t  stand 
very  well  with  the  master,  you  were  at  least  in  high 
favour  with  the  boys,  Humphry,  for  you  used  to  do 
the  Latin  and  English  verses  for  half  the  school ; 
and  as  for  writing  valentines  and  love-verses,  why 
I am  sure  your  play-time  was  mostly  taken  up  with 

that  he  appeared  before  Mr.  Coryton  with  a large  plaster  on  each 
ear,  and  that  when  asked  by  his  master  ‘ what  was  the  matter 
with  his  ears,’  he  replied  with  a very  grave  face,  k that  he  had 
put  the  plasters  onto  prevent  a mortification.’” — Dr.  John  Davy, 
p.  14.  In  a letter  to  his  mother,  Sir  Humphry  Davy  says,  speak- 
ing of  this  school,  “ I consider  it  fortunate  that  I was  left  much 
to  myself  as  a child,  and  put  upon  no  particular  plan  of  study, 
and  that  I enjoyed  much  idleness  at  Mr.  Coryton’s  school.  I 
perhaps  owe  to  these  circumstances  the  little  talents  that  I have, 
and  their  peculiar  application.  What  I am,  1 have  made  myself. 
I say  this  without  vanity,  and  in  pure  simplicity  of  heart.”  Davy 
seems,  indeed,  to  have  been  more  distinguished  out  of  school, 
and  by  his  comrades,  than  by  any  great  advance  in  learning. 
“From  his  facility  in  composing  Latin  and  English  verse,”  says 
his  brother,  “ his  assistance  in  these  exercises  was  often  request- 
ed, even  by  boys  much  older  than  himself;  and  in  writing  valen- 
tines and  love-letters,  he  shone  so  pre-eminently,  and  gave  his 
aid  so  willingly,  that  he  is  said  to  have  been  generally  resorted 
to  on  all  emergencies  of  boyish  loves.  Another  cause  of  popu- 
larity among  his  comrades  was  his  power  of  diverting  them  by 


HUMPHRY  AND  HIS  MOTHER. 


63 


scribbling  rhymes  to  first  Miss  This  and  then  Miss 
That  for  some  little  urchin  in  a jacket,  who  fancied 
himself  to  be  smitten  with  the  young  lady.  Then 
of  an  evening  you  were  always  to  be  found  under 
the  balcony  of  the  Star  Inn — for  you  were  shel- 
tered there — with  a group  of  boys  round  about  you ; 
and,  if  there  happened  to  be  a cart  on  the  spot,  you 
would  be  sure  to  mount  it,  and  there  you’d  remain 
narrating  all  kinds  of  romantic  stories  to  the  little 
mob  of  school-fellows  who  came  regularly  to  listen 
to  you.  I never  knew  such  a boy  for  story-telling 
as  you  were,  Humphry ! I have  many  a time  heard 
you  make  up  the  strangest  kind  of  tales  out  of  your 
own  head ; and  while  I was  in  the  parlour  at  work, 

telling  them  stories  ; and  so  attractive  were  the  tales,  commonly 
of  wonder  and  terror,  which  he  related,  that  they  were  in  the 
habit  in  an  evening  of  collecting  at  a particular  place  to  wait  for 
him,  as  under  the  balcony  of  the  Star  Inn,  which  afforded  shelter, 
and  where,  if  there  happened  to  be  a cart,  he  would  get  into  it, 
and  hold  forth  to  his  young  audience.”  {Idem,  p.  15.)  “ The 

earliest  indication  that  I am  aware  of,”  says  Davy’s  brother, 
“ which  he  showed  of  his  fondness  for  experimenting,  was  in 
making  fire-works.  My  eldest  sister  well  remembers  that  she 
was  his  assistant  in  this  undertaking,  and  that  their  workshop 
was  an  unfurnished  room,  in  which,  in  bad  weather,  the  Rev.  Dr. 
Tonkin  (the  elder  brother  of  Mr.  John  Tonkin,  the  friend  of  our 
family),  then  advanced  in  age  and  a valetudinarian,  took  exer- 
cise on  his  chamber-horse — a large  arm-chair  attached  to  spring- 
boards, which  boards  served  for  a table  for  compounding  the  in- 
gredients of>the  squibs  and  crackers.”  “ Davy,”  says  Dr.  Paris, 
speaking  of  his  youthful  amusements,  “was  in  the  habit  of  pre- 
paring a detonating  composition,  to  which  he  gave  the  name  of 
‘thunder  powder,’  and  which  he  would  explode  on  a stone,  to 
the  great  delight  of  his  young  playfellows”  (p.  5). 


64 


THE  WONDERS  OF  SCIENCE. 


I used  to  listen  to  you,  as  you  and  young  Batten 
sat  out  in  the  porch,  with  your  arms  curled  round 
each  other’s  necks,  and  you  would  be  there  hour 
after  hour;  for  you  were  never  tired  of  inventing, 
nor  he  tired  of  listening  to  the  stories  of  wonder 
and  terror  you  both  delighted  in.” 

“I  can  remember  it  all  well,  mother,”  added 
Humphry.  “ And  do  you  recollect  how  fond  I was 
of  making  fire-works,  and  how  Kitty  used  to  help  me 
till  her  fingers  were  as  black  as  sticks  of  liquorice 
with  the  gunpowder ; and  how  we  used  to  mix  up 
the  composition  for  our  squibs  and  crackers  on  the 
spring-boards  of  old  Dr.  Tonkin’s  chamber-horse 
that  stood  in  the  empty  room,  when  we  lived  at 
Penzance,  and  that  the  poor  old  gentleman  used  to 
take  his  exercise  upon  in  wet  weather  ?” 

“Yes,  that  I do,  Humphry,”  smiled  Mrs.  Davy; 
“and  many  a time  you  have  nearly  frightened  me 
out  of  my  wits  with  your  4 thunder-powder,’  as 
you  called  it,  which  you  used  to  delight  in  putting 
under  the  chairs,  so  that  the  moment  any  one  sat 
down,  there  was  such  an  explosion  that  everybody 
in  the  room  felt  as  though  all  their  bones  had 
been  suddenly  broken.  Your  poor  father  only  per- 
ceived in  such  tricks  an  idle,  thoughtless  disposi- 
tion ; but  women  see  more  keenly  into  character 
than  men,  and  I not  only  recollected,  but  knew,  the 
quick  boy  you  were,  and  how  rapidly  you  could 
acquire  anything  to  which  you  applied  yourself; 


HUMPHRY  AND  HIS  MOTHER. 


65 


besides,  I had  noticed  your  inventive  turn  from 
a child,  and  the  force  of  your  imagination  in  the 
stories  you  made  up  and  the  poems  you  had  writ- 
ten— for  at  twelve  you  had  composed  an  epic  that 
I have  by  me  still — and  all  these  things  gave  me 
assurances  that  one  day  you  would  take  a foremost 
place  among  the  great  men  of  the  country.  A 
mother’s  heart  may  have  led  me  to  have  these 
hopes  of  you,  Humphry ; my  understanding,  how- 
ever, convinced  me  that  they  were  not  mere  dreams 
begotten  by  affection,  but  conclusions  calmly  come 
to  after  narrowly  watching — as  a mother  only  can 
watch — every  little  turn  and  trait  in  your  cha- 
racter.” 

u No,  mother !”  burst  out  the  boy ; “ they  are 
not  dreams,  but  clear  foreseeings ; and  you  yourself 
shall  witness  the  realisation  of  them  before  many 
years  have  passed.” 

“ God  grant  that  I may  live  to  do  so,  my  boy,” 
murmured  the  widow,  as  she  raised  her  eyes  to 
heaven.  “ ‘ Life,’  as  some  wise  man  says,  4 has 
few~  better  things  to  give  than  a talented  son,’  and 
it  seems  to  me  there  can  be  no  greater  pleasure 
to  a mother’s  heart  than  to  witness  the  genius 
which  she  lias  watched  bud  and  expand  from  year 
to  year  ripen  into  excellent  wisdom,  and  come  to 
be  acknowledged  and  reverenced  by  the  world  at 
large — no  joy  more  exquisite  to  a woman’s  nature 
than  that  which  she  must  surely  experience  on 

E 


66 


THE  WONDERS  OF  SCIENCE. 


finding  that  the  mind  which  she  had  tended  from 
its  very  dawn — catching  up  the  first  glimpses  of  in- 
tellect, and  garnering  them  in  her  bosom  as  house- 
hold wonders  and  bright  things  of  promise — has 
fulfilled  all  her  best  hopes,  and  that  the  visions  she 
had  formed  of  the  fame  and  honour  that  were  to 
attend  her  boy  in  after-life  have  not  been  mere 
dreams  of  her  admiration  or  her  pride.  But  ra- 
ther, that  the  being  whom  she  has  loved,  and  wish- 
ed to  have  loved  by  others,  lives  to  be  at  length 
praised  and  esteemed  by  all,  for  the  talents  and 
virtues  that  she  was  the  first  to  notice  and  to  fos- 
ter. This,  Humphry,  is  the  brightest  and  sweetest 
reward  a woman  can  meet  with  in  her  old  age ; 
and,  having  reaped  it,  she  parts  from  life  with  a 
sense  of  duty  fulfilled,  and  a feeling  that  the  affec- 
tion with  which  she  welcomed  her  child  into  ex- 
istence, and  the  care  with  which  she  tended  him  in 
his  youth,  have  not  been  unprofitably  bestowed,  but 
repaid  her  in  the  richest  coin  the  world  can  offer  to 
a parent.” 

Humphry  for  a while  remained  in  silence,  while 
his  mother’s  words  sank  deep  into  his  soul;  then 
he  said,  softly,  “ May  it  be  my  proud  lot,  mother, 
to  render  you  such  a reward.  I am  thankful  to 
the  Creator  that  I have  passed  through  the  most 
dangerous  portion  of  my  life  with  few  errors,  and 
I hope  to  devote  myself  for  the  future  to  pursuits 
useful  to  mankind,  and  which  in  after  years  may 


HUMPHRY  AND  HIS  MOTHER. 


67 


perhaps  obtain  for  me  the  applause  of  enlightened 
men.”* 

The  widow  laid  her  hand  on  the  boy’s  head  as  he 
sat  at  her  feet,  and  she  said,  solemnly,  “ My  blessing 
be  on  you,  my  son.  May  God  give  you  strength  to 
maintain  your  noble  purpose !” 

Then  she  threw  her  arms  about  him,  and  burst- 
ing into  a flood  of  tears,  cried,  u Oh,  my  boy ! my 
boy ! you  know  not  how  happy  you  have  made 
me.  Your  words  are  like  oil  to  my  wounded  heart. 
Sometimes,  of  late,  I have  wondered  why  it  should 
please  Providence  to  visit  me  so  sorely — me , who 
never  knowingly  injured  any  one  in  thought  or 
act.  And  yet,  even  almost  in  my  infancy,  I was 
deprived  of  father  and  mother  at  one  blow,  so 
that  the  very  features  of  my  parents  are  unre- 
membered by  me,  and  the  blessing  of  their  love 
a joy  I was  scarcely  allowed  to  taste.  And  now, 
before  my  own  children  are  able  to  help  them- 
selves, he  who  would  have  been  their  best  pro- 
tector is  snatched  from  me,  and  I again  am  alone 
in  life,  bereft  of  the  love  and  care  I had  hoped 

* The  above  are  Davy’s  own  words,  taken  from  a fragment  of 
a letter  which  his  brother  says  exists  in  one  of  Sir  Humphry’s 
note-books,  kept  during  his  youth,  and  which  was  addressed  to 
one  of  his  early  home  friends,  the  letter  itself  being  descriptive 
of  his  escape  from  the  vices  which  are  the  most  seductive  to 
youth  in  towns.  “ An  active  mind,”  he  writes,  “a  deep  ideal 
feeling  of  good,  a look  towards  future  greatness,  has  preserved  me 
from  these.” 


68 


THE  WONDERS  OF  SCIENCE. 


to  share  for  years  to  come,  and  left  with  five 
young  children,  and  only  a woman’s  arm  to  shield 
them  from  the  buffetings  of  the  world.  It  needs 
no  little  faith  in  the  goodness  of  God,  Humphry, 
to  believe  that  there  is  a mercy  in  all  this ; and  oft- 
en, in  the  bitterness  of  my  tribulation,  I have  been 
vricked  enough  to  doubt  it:  for  I,  with  my  mind 
distempered  by  suffering,  could  discover  no  trace  of 
kindness  in  it  all.  But  now  I see  the  purpose  of 
my  affliction.  It  was  to  stir  you,  Humphry,  to  be 
a protector  to  your  brother  and  sisters — to  develop 
the  high  and  noble  nature  with  which  you  had  been 
gifted,  and  to  raise  up  to  me  a son,  the  glory  of 
whose  future  renown  should  be  something  like  a 
recompense  to  me  for  the  partner  I have  lost — a son 
who  should  be  the  means  of  contributing  not  only 
to  the  comfort  and  happiness  of  my  children,  but  to 
the  welfare  of  mankind  at  large.  Yes  ! I under- 
stand the  reason  of  my  trials  now : and  look  you, 
my  dear  boy,  how  good  comes  of  evil.  The  first 
privation  I and  your  aunts  suffered  was  the  means 
of  creating  for  us  such  a friend  as  is  seldom  met 
with  in  this  world  ; I mean  Mr.  Tonkin,  who  was 
not  only  a father  to  me  and  my  sisters,  but  has  ex- 
tended his  goodness  to  our  children — for  you,  Hum- 
phry, have  passed  more  of  your  time  with  him  than 
under  your  poor  father’s  roof.  And  now,  no  sooner 
is  my  husband  taken  from  me  than  you — the  giddy 
boy,  who  had  of  late  been  so  absorbed  in  pleasure 


HUMPHRY  AND  HIS  MOTHER.  69 

1 

that  I had  almost  begun  to  think  the  hopes  I had 
formed  were  nothing  but  a mother’s  vanity — be- 
come quickened  in  an  instant  with  a new  nature, 
as  if  suddenly  exalted  into  manhood,  instinct  with 
generous  purposes  and  noble  determinations;  and, 
though  you  are  but  a mere  youth  in  years,  ready  to 
supply  the  place  of  a father  to  your  brother  and  sis- 
ters, and  a friend  and  protector  to  me.” 


CHAPTER  IV. 


THE  FIRST  DRINK  AT  THE  WELL. 

A few  months  had  wrought  a great  change  in 
the  household  at  Varfell. 

The  widow,  when  the  stupor  of  her  grief  had 
passed  away,  and  the  mental  absorption  of  her  first 
sorrow  had  given  place  to  the  calm  reflection  of 
melancholy,  soon  began  to  see  that  the  comforts  and 
education  of  her  children  demanded  energy  rather 
than  tears  from  her. 

Then  came  the  struggle.  What  could  she  do  to 
help  them  ? And  what  would  the  people  think  and 
say  if  this  or  that  were  done? 

But  Mrs.  Davy  was  not  the  woman  to  be  daunt- 
ed by  the  petty  exultation  of  neighbours ; so  that 
when  an  opportunity  offered  for  her  to  embark  in 
business  as  a milliner  in  the  neighbouring  town, 
it  cost  her  hardly  a pang — free  as  she  was  from 
all  silly  pride — to  sink  from  the  worldly  rank  of 
the  gentlewoman  into  the  humbler  station  of  the 
trader. 


THE  FIRST  DRINK  AT  THE  WELL. 


71 


Accordingly,  after  consulting  with  Mr.  Tonkin 
upon  the  matter,  she  was  duly  installed,  in  con- 
junction with  a young  French  lady,  as  dressmaker 
and  milliner,  in  a little  shop  in  the  town  of  Pen- 
zance. 

Nor  was  Humphry  long  in  finding  a fitting  occu- 
pation. Mr.  Tonkin,  to  whom  the  youth  had  com- 
municated all  his  determinations,  and  who  loved 
the  youth  almost  as  if  he  had  been  a child  of  his 
own  (for  the  greater  part  of  Humphry’s  life  had 
been  passed  with  the  old  gentleman),  was  as 
pleased  as  the  widow  had  been  to  hear  of  the  new 
spirit  that  had  come  upon  the  lad ; and  although 
the  boy’s  foster-father  was  not  so  sanguine  as  his 
mother  had  been  of  the  world-wide  renown  that 
awaited  Humphry  in  after  life,  he  had,  neverthe- 
less, sufficient  faith  in  the  talents  of  the  youth  to 
believe  that  he  might,  by  application,  ultimately  win 
his  way  to  competence  and  respect  among  the  cir- 
cle of  his  native  town.  Accordingly,  when  the  ar- 
dent boy  spoke  to  the  calm  old  man  of  the  fame 
and  honours  he  had  made  up  his  mind  to  gain 
throughout  Europe — saying,  with  all  the  fervour  of 
a boy-poet’s  nature,  that  he  was  resolved  his  mind 
should  become  a light  to  all  nations,  and  that  his 
name  should  be  linked  with  noble  associations  in 
every  enlightened  country,  Mr.  Tonkin  smiled  in- 
credulously (but  still  with  good  humour)  at  the 


72 


THE  WONDERS  OF  SCIENCE. 


ambitious  dreams  of  the  lad,  and  told  him  he  was 
afraid  one  so  young  as  he  knew  not  how  difficult  it 
was  to  excel,  even  in  the  most  trivial  thing,  when 
we  had  the  entire  world  for  rivals;  and  that  pow- 
ers which  appeared  great  in  the  narrow  circle  of 
our  own  family,  grew  less  and  less  as  the  arena 
of  competition  was  widened.  Therefore,  if  the 
youth,  instead  of  regarding  the  whole  of  Christen- 
dom as  the  theatre  in  which  his  future  powers 
were  to  be  displayed,  would  but  limit  his  views 
to  the  humble  town  of  Penzance,  Mr.  Tonkin  said 
he  thought  Humphry  might,  with  industry  and 
prudence,  some  day  attain  a reputable  position 
in  the  neighbourhood  ;*  adding,  that  he  should 
consider  himself  well  rewarded  for  the  care  and 

* When  Davy  was  offered  the  appointment  of  Superintendant 
of  the  Pneumatic  Institution  at  Bristol,  “he  accepted  it,”  says 
his  brother,  “ with  the  consent  of  all  his  friends,  excepting  Mr. 
John  Tonkin,  who  had  hoped  he  would  have  settled  at  Penzance  ; 
and  who,”  Dr.  Davy  tells  us  in  another  place,  “was  so  angry 
with  Humphry  for  accepting  the  appointment,  that  he  made  some 
alteration  in  his  will  in  consequence.”  Dr.  Paris’s  version  of  the 
affair  is  as  follows : “ His  old  and  valued  friend,  Mr.  Tonkin, 
not  only  expressed  his  disapprobation  of  the  scheme,  but  was  so 
vexed  and  irritated  at  having  his  favourite  plan  of  fixing  Davy  in 
his  native  town  as  a surgeon  thus  thwarted,  that  he  actually  alter- 
ed his  will,  and  revoked  the  legacy  of  his  house,  which  he  had 
previously  bequeathed  him.  Mr.  Tonkin  died  on  the  24th  De- 
cember, 1801 ; so  that,  although  he  lived  long  enough  to  witness 
Davy’s  appointment  to  the  Royal  Institution,  he  could  never  have 
anticipated  the  elevation  to  which  his  genius  and  talents  ultimately 
raised  him." — Life  of  Sir  Humphry  Davy , p.  30. 


THE  FIRST  DRINK  AT  THE  WELL. 


73 


affection  he  had  bestowed  upon  Humphry  if  he 
should  live  to  see  him  settled  as  a surgeon  in  his 
native  town. 

It  was  a lovely  autumn  evening — such  an  even- 
ing as,  at  the  decline  of  the  year,  is  known  only  in 
those  parts  of  our  island  which,  from  the  mildness 
of  their  climate,  have  been  styled  “ the  Florence  of 
the  North.”  Mr.  Tonkin  and  Humphry  had  stroll- 
ed out  by  Marazion  towards  St.  Michael’s  Mount, 
journeying  along  the  curved  shore  of  the  magnifi- 
cent bay,  with  the  ocean  spread  out  on  one  side,  in 
a broad  expanse  of  unsullied  azure,  and  fringed 
with  a thin  border  of  silver  foam,  as  the  waves 
came  rippling  lazily  over  the  yellow  sands.  As 
they  sauntered  along,  the  breeze  at  sundown  began 
to  set  from  the  land  towards  the  ocean,  and,  sweep- 
ing across  the  warm  earth,  it  came  laden  with  the 
perfumes  of  the  many  exotics  that  bloom  in  'the 
open  air  in  that  part  of  the  world — the  garden  of 
England  ; for  it  was  just  the  hour  when  the  flowers 
love  to  pour  their  odours  into  the  lightened  air, 
like  incense  from  a thousand  chalices.  The  rays 
of  the  declining  sun  gave  a faint  tint  of  purple  to 
the  atmosphere,  and  the  green  sward,  that  was  still 
lustrous  with  the  slanting  light,  was  striped,  here 
and  there,  with  the  long  shadows  that  streamed 
from  every  object  intercepting  the  beams;  while 
the  outlines  of  each  form  were  growing  more  and 


74 


THE  WONDERS  OF  SCIENCE, 


more  definite,  and  the  sides  and  peaks  of  the  rocks 
glittered  towards  the  west,  as  if  they  were  blazoned 
with  red  gold.  The  brown  cattle  were  quiet  in  the 
fields,  and  the  tranquil  flocks  on  the  distant  hillsides 
rested  there  like  clouds ; the  branches  of  the  trees 
beside  the  roadway  were  shaggy,  almost  to  the  tops, 
with  the  long  stalks  of  wheat  that  dangled  from  the 
twigs,  telling  of  some  high-laden  harvest-waggon  that 
had  lately  swept  by  them.  The  white-bellied  swal- 
lows skimmed  low  over  the  earth  in  zigzag  lines, 
twittering  as  they  went ; and  there  was  a soothing 
stillness  all  around  that  bathed  the  soul  in  balmy 
quietude. 

Towards  the  sea  the  scene  was  no  less  beautiful. 
The  ocean  was  like  a huge  green  gem,  and  here 
and  there  on  its  surface  tiny  boats  seemed  to  revel 
in  the  sundown  breeze,  now  that  it  had  sprung  up, 
and  leant  over  on  one  side,  as  they  went  plough- 
ing through  the  liquid  field,  turning  up  the  white 
surf  on  their  way,  and  leaving  far  behind  them 
a long  trail,  that  looked  in  the  distance  like  a 
seam  upon  the  water ; while  in  the  offing  tall  ships 
stood  against  the  sky,  with  their  sails  pouting  and 
shining  white  in  the  sun,  like  a pigeon’s  breast. 
Nearer  the  shore  rose  the  majestic  rocky  mount  of 
St.  Michael,  towering  above  the  sea  like  one  of 
Nature’s  pyramids,  with  the  broken  outline  of  its 
ivied  sides  showing  sharp  and  clear  against  the 
grey,  ariel  distance;  one  half  of  it,  towards  the 


THE  FIRST  DRINK  AT  THE  WELL. 


75 


east,  was  dusked  in  deep  rich  shadow,  while  the  oth- 
er, towards  the  west,  was  bathed  in  such  a glory  of 
ruby  light,  that  the  Mount  shone  as  if  it  had  been 
one  huge  carbuncle  studding  the  bright  shield  of  the 
ocean.  Then,  in  the  far  west,  the  sky  and  the  sea 
were  as  a sheet  of  molten  gold ; and,  almost  resting 
on  the  ring  of  the  horizon,  was  seen  the  round,  liquid 
orb  of  the  sun,  trembling  like  a well  of  light,  with 
the  broad  beams  streaming  upwards  from  it,  and 
tinting  the  distant  masses  of  cloud,  now  ruby  and 
now  purple,  till  they  looked  like  islands  of  garnet  and 
amethyst  in  the  heavens. 

It  was  low  water,  and  the  couple  crossed  by  the 
sands  from  Marazion  to  the  Mount ; and  here,  after 
passing  the  little  cluster  of  fishermen’s  houses  that 
skirted  the  base  of  the  rocky  pyramid,  and  mount- 
ing a short  distance  up  the  cliff,  they  sat  for  a while 
enjoying  and  discoursing  of  the  many  beauties  of 
the  majestic  scene  that  encompassed  them  on  every 
side. 

And  the  prospect  thence  was  indeed  of  the  grand- 
est character.  The  shore  stretched  away,  revealing 
headland  after  headland,  to  where  the  Lizard  shot 
out  far  into  the  wave,  the  rocks  there  seeming  al- 
most phosphorescent  in  the  sun.  Then  appeared  St. 
Clement’s  Island  and  the  coast  towards  the  Land’s 
End,  forming  a shorter  cape,  and  completing  the 
horn  of  the  crescent  of  land  towards  the  west,  that 
looked,  as  the  waves  grew  crimson  in  the  sunset,  as 


76 


THE  WONDERS  OF  SCIENCE. 


if  bathed  in  a sea  of  wine.  The  ocean  here  wore  its 
most  imposing  attribute  of  uncontrollable  immens- 
ity; for  the  Atlantic,  across  the  Bay  of  Biscay  to 
the  most  western  land  of  Spain,  lay  on  the  south, 
and  melted  into  distance  there ; while,  beyond  the 
extremity  of  our  own  island,  no  shore  intervened  on 
the  north  between  the  line  of  the  horizon  and  the 
land  of  the  New  World. 

* 

It  was  a sight  that  Humphry  loved  as  deeply  as 
old  Mr.  Tonkin  to  look  upon,  and  the  couple  sat  for 
some  time  silently  watching  both  the  seas  rolling 
there  towards  the  far  distant  Spanish  and  American 
shores. 

The  boy,  however,  less  capable  of  continuous  at- 
tention to  the  same  subject,  got  to  weary  of  the  scene 
sooner  than  the  old  man ; and  when  Mr.  Tonkin  no- 
ticed Humphry’s  admiration  begin  to  flag,  he  availed 
himself  of  the  quietude  of  the  time  and  place  to  incite 
a taste  in  the  lad  for  the  profession  he  washed  him 
to  follow. 

Presently  the  old  doctor  caught  sight  of  one  of  the 
little  transparent  zoophytes  that  had  been  left  on  the 
rocks  by  the  receding  tide.  In  size  it  was  not  larger 
than  a bird’s  egg,  of  a globular  form,  with  several 
transparent  ridges  ranged  along  it,  from  pole  to  pole, 
as  it  were,  and  it  was  nearly  as  pellucid  as  the  purest 
rock-crystal. 

“ Look,  my  boy,”  said  Mr.  Tonkin,  turning  to 
Humphry,  and  pointing  to  the  little  ball  of  jelly  at 


/ 


THE  FIRST  DRINK  AT  THE  WELL.  79 

iiis  feet ; “ here  is  an  orb  almost  as  wonderful  as  the 
sun  we  have  been  lately  gazing  at.  It  gives  light, 
too,  like  it ; and  though  it  looks  there  as  if  it  were 
only  a few  drops  of  the  ocean  gelatinised,  it  is  quick- 
ened with  life,  and  performs  motions  that  our  wisest 
engineers  can  but  clumsily  imitate.” 

The  eager  boy  was  about  to  seize  the  wonder,  so 
that  he  might  examine  it  more  minutely. 

“ Nay,  if  you  touch  it,”  cried  the  old  man,  hastily, 
as  he  grasped  the  youth’s  arm,  and  held  him  back, 
<£  it  will  immediately  dissolve — thaw,  as  it  were,  to 
death — so  frail  is  its  life,  and  nothing  but  a little 
pool  of  water  will  remain  of  a creature  that  once 
could  make  the  sea  glow  with  its  fire.  These  little 
things  are  by  some  styled  thd  1 lucid  gems  of  the  wa- 
ters.’ By  daylight,  when  in  the  ocean,  they  are  visi- 
ble only  by  the  bright  rainbow  hues  that  mark  their 
path  as  they  paddle  along ; but  by  night,  Humphry, 
they  blaze  with  phosphorescent  fire,  so  that  some 
have  termed  them  4 the  stars  of  the  sea.’  In  warm 
and  calm  evenings  they  often  look  like  balls  of  light 
rolling  on  the  surface  of  the  water,  and  the  more 
rapid  their  motion  the  more  intense  is  the  glow 
they  emit.  Those  eight  transparent  ridges  you  see 
there,”  continued  the  doctor,  as  he  pointed  with  his 
cane  to  the  tiny  watery  globe,  “ support  as  many 
rows  of  broad,  pellucid  paddles,  and  these  are  all  in- 
stinct with  life,  and  by  their  rapid  motion  cause  the 
animal  to  glide,  meteor-like,  through  the  waves.  We 


80 


THE  WONDERS  OF  SCIENCE. 


wonder  at  the  recent  invention  of  the  steam-boat, 
and  speak  with  pride  of  the  paddle-wheels  with 
which  we  are  to  walk  upon  the  waters ; but  the  tiny 
paddles  here,  boy,  are  far  more  perfect  than  any 
ever  contrived  by  human  ingenuity,  for  in  that  little 
aqueous  ball  the  cumbrous  machinery  which  is  re- 
quired to  move  our  vessels  along,  is  not  needed,  since 
each  float,  self-moving  without  even  a visible  muscle 
or  nerve  to  stir  it,  keeps  time  with  all  the  rest.”* 

“ What  wonder,”  cried  the  poetic  boy,  “ is  here 
packed  in  a little  living  crystal,  as  it  were,  that  can 
make  fire  flash  from  what  looks  almost  like  a globe 
of  water,  and  that  can  perform  the  most  rapid  mo- 
tions without,  as  you  say,  Mr.  Tonkin,  any  visible 
means  of  movement !” 

“ Yes,  indeed,  my  lad,”  went  on  the  old  man ; 
“ there  is  a large  store  of  marvels  locked  in  that  lit- 
tle glassy  casket.  How  does  it  get  its  food  ? How 
digest  it  % and  how  is  its  frail  body  nourished  for 
we  can  trace  no  blood-vessels,  nor  heart,  nor  glands 
— indeed,  hardly  any  organs  at  all  — in  the  little 
clot  of  half-liquid  life.  All  we  know,  is,  that  it 
is  furnished  underneath  with  so  many  tentacles 
or  filaments,  that  serve  it  for  claws,  and  that 
these,  which  are  set  round  an  aperture  that  we 
call  a mouth,  draw  the  food  it  lives  upon  into  its 

* The  little  zoophyte  here  described  is  a kind  of  small  “jelly- 
fish” known  by  the  name  of  the  “ Beroe.”  It  may  be  often  seen 
on  our  shores. 


THE  FIRST  DEINK  AT  THE  WELL. 


81 


body — which  is  literally  nothing  but  a stomach.  If 
we  were  to  watch  long  enough,  we  should  see  the 
food  thus  seized  and  swallowed  gradually  dissolve 
and  be  reduced  to  a fluid  state,  while  the  more 
solid  and  indigestible  portion  would  be  rejected  by 
the  aperture  through  which  it  entered.  The  nutri- 
tive matter  we  know  to  be  absorbed  by  the  walls  of 
the  stomach,  every  part  of  which  appears  to  be  en- 
dowed with  equal  power  in  this  respect ; and  it  is 
then  conveyed  to  the  remoter  portion  of  the  body 
by  the  simple  inbibition  of  one  part  from  another, 
without  any  proper  circulation  through  vessels.  In 
some  animals  of  this  class  the  external  covering  of 
the  body  and  the  lining  of  the  stomach  so  closely 
correspond  in  their  structure  as  to  admit  of  being 
changed  one,  for  the  other — for  the  animal  may  be 
turned  inside  out  without  its  functions  being  in  any 
way  deranged.” 

“ Can  it  be  V*  said  Humphry,  filled  with  delight. 
“ Where  can  I learn  these  things,  sir  ? Why  was  I 
not  taught  them  at  school?” 

“You  shall  learn  them,  my  boy,”  replied  the  old 
man,  pressing  the  lad’s  hand  with  pleasure  to  find 
the  taste  that  he  had  longed  to  develope  for  his  own 
favourite  study  springing  up  in  Humphry’s  mind. 
“And  think,  if  that  little  lump  of  jelly — which  is, 
perhaps,  the  simplest  form  of  life,  where  the  vital 
mechanism  is  seen  in  its  rudest  form — can  stir  you 
to  so  much  wonder— think,  I say,  Humphry,  what 


82 


THE  WONDERS  OF  SCIENCE. 


admiration  will  be  excited  in  you  when  you  come 
to  comprehend  the  beautiful  processes  and  organism 
exhibited  in  complicate  animals  like  ourselves ! If 
a living,  digesting  creature— a thing  almost  without 
sense — a mere  moving  mouth — can  appear  so  won- 
derful to  you  in  its  structure,  what  marvels  shall 
you  not  find  in  the  constitution  of  a thinking,  speak- 
ing, reasoning  being  like  man !” 

Then  the  old  doctor  ran  over  to  the  youth  the 
many  sources  of  knowledge  that  the  study  of  hu- 
man life  opens  up  to  the  thoughtful  and  inquiring 
mind. 

He  told  the  eager  boy — as  they  sat  there  in  the 
subdued  light  of  the  evening,  with  the  hum  of  the 
sea  that  rippled  into  the  caverns  at  the  base  of  the 
Mount,  falling  almost  musically  on  the  ear — how,  in 
the  organism  of  the  nerves  and  brain,  we  get  our 
first  insight,  rude  though  it  be,  into  the  subtle  pro- 
cesses of  the  senses,  and  even  the  mind  itself.  He 
told  him,  also,  how,  in  the  senses  themselves,  lay 
the  rudiments  of  all  the  sciences ; how,  without  the 
sense  of  vision,  there  could  have  been  no  44  optics,” 
and  consequently  no  astronomy — for  to  the  blind 
the  movements  of  the  planets,  and  even  the  very 
existence  of  the  stars,  must,  of  course,  have  remain- 
ed unknown : in  like  manner,  without  the  sense  of 
hearing  there  could  have  been  no  44  acoustics”  and 
no  music;  and  without  the  sense  of  muscular  effort 
r.o  knowledge  of  weight,  and  consequently  of  44  gra- 


THE  FIRST  DRINK  AT  THE  WELL. 


83 


vitation” — the  main-spring,  as  it  were,  of  the  mech- 
anism of  the  universe. 

Mr.  Tonkin  explained  to  the  youth,  moreover,  that 
had  we  been  formed  without  the  exquisite  organ  of 
the  hand  there  would  have  been  little  work  done, 
and  but  little  art  achieved  ; and  without  the  organs 
of  the  mouth,  there  could  have  been  no  inter-com- 
munication of  thought — no  transfusion  of  mind  into 
mind,  by  which  one  wise  man  now-a-days  contains 
stored  in  his  own  brain  the  wisdom  of  almost  all 
those  who  have  preceded  him.  And  further,  if  we 
had  had  no  appetites,  and  no  pains  nor  uneasinesses 
to  stir  us  to  action,  we  should,  even  with  the  beau-  - 
tiful  muscular  apparatus  with  which  our  frames  are 
fitted,  have  remained  idle  and  inactive  all  our  time, 
starving  to  death  with  delight. 

“ Some  persons,”  said  Mr.  Tonkin,  “ have  sup- 
posed that  plants  may  be  susceptible  of  feeling,  as 
well  as  ourselves  and  the  rest  of  the  animal  race. 
But  that  trees  and  herbs  are  incapable  of  knowing 
either  pain  or  pleasure”  (he  added)  “is  made  evi- 
dent, physiologically,  by  the  fact  that  they  are  sup- 
plied with  no  organs  of  locomotion,  and  conse- 
quently deprived  of  the  means  of  avoiding  the  one 
and  seeking  the  other.  For,  so  benevolently  is  the 
world  arranged,  that  wherever  feeling  is  given,  the 
power  of  acting  is  immediately  associated  with  it; 
indeed,  it  requires  hardly  a moment’s  thought  to 
perceive  that  it  would  have  been  incompatible  with 


84 


THE  WONDERS  OE  SCIENCE. 


All-Kindness  to  have  made  creatures  sensible  to 
pain,  and  yet  have  denied  them  the  means  of  escape 
from  it.” 

After  this  the  old  man  pointed  out  to  Humphry, 
that  in  the  comparison  of  one  system  of  life  with 
another,  and  so  tracing  the  delicately  interwoven 
chain  of  animal  creation,  we  perceive  that  the  first 
type  of  sentient  existence  was  a mere  stomach- — a life 
of  pure  appetite — susceptible  of  no  other  feeling  than 
hunger,  and  fitted  only  with  organs  for  seizing  and 
assimilating  its  food ; while  as  we  advance  gradual- 
ly in  the  scale  of  development,  we  find  nerve  after 
nerve  added,  and  a new  set  of  feelings  and  actions 
brought  out,  with  each  new  set  of  fibres.  “We  dis- 
cover, besides,”  he  continued,  “that  when  a little 
kernel  of  nervous  matter  was  superadded  to  the 
previous  sentient  apparatus,  the  wondrous  sense  of 
vision  was  first  awakened  in  animal  life,  and  how 
the  addition  of  another  such  little  kernel  made  an 
animal  for  the  first  time  hear,  and  another  gave  the 
first  sense  of  odour  to  the  world,  while  another  add- 
ed taste  to  the  food  and  drink.” 

And  when  he  had  thus  briefly  explained  to  the 
youth  the  uses  and  characteristics  of  the  several 
organs  in  man  and  the  lower  animals,  the  old 
gentleman  went  on  to  point  out  to  him  how  these 
same  organs  were  nourished,  and  the  destruction 
that  was  continually  going  on  in  the  body — 
“ for,”  said  he.  “ we  cannot  move  a muscle,  not  even 


THE  FIRST  DRINK  AT  THE  WELL. 


85 


wink  our  eyelids,  without  wasting  some  tissue  or 

\ 

other” — was  being  as  continually  repaired  by  the 
food  consumed.  Pursuing  this  subject,  he  then 
proceeded  to  explain  to  young  Humphry  how  the 
blood  was  made  to  circulate  by  means  of  the  cun- 
ningly-wrought chambers  of  the  heart  through  the 
veins  and  arteries,  distributing  health  and  vigour 
to  the  different  organs  in  its  course — now  renova- 
ting the  tissues,  now  depositing  little  specks  of  bone, 
then  extending  the  filaments  of  hair,  and  then  ex- 
citing thought  and  developing  feeling  in  the  nerves 
and  brain,  stimulating  action  in  the  muscles,  and 
diffusing  warmth  throughout  the  whole  frame- 
all  these  different  functions  being  performed  by  the 
one  wondrous  substance  in  which,  even  when  ex- 
amined by  the  highest  microscopic  power,  it  was 
impossible  to  detect  even  the  rudiments  of  the  many 
various  tissues  it  formed. 

“ Such,”  said  Mr.  Tonkin,  “ is  a part  of  the  mar- 
vellous process  of  secretion — a process  so  subtle  that 
even  the  wisest  can  only  wonder  in  their  ignorance 
concerning  the  function  ; for  it  is  a mystery  to  them 
how,  by  means  merely  of  little  glands,  so  many 
different  things  can  be  produced  from  one  and  the 
same  fluid.  How,  for  instance,  skin,  cartilages, 
muscles,  hair,  nails,  bones,  tears,  and  the  infinite 
variety  of  products  which  our  bodies  are  made  up 
of  and  evolve,  can  all  come  from  the  same  ruby 
stream,  and  that  a small  nut-like  organ  only  shall 


86 


THE  WONDERS  OF  SCIENCE. 


be  necessary  to  eliminate  each  different  substance 
from  it.  Then,  again,  there  is  the  beautiful  pro- 
cess of  breathing,  by  which  the  vital  air  is  com- 
bined with  the  blood,  and  the  blue  fluid  of  the  veins 
changed  into  the  crimson  stream  of  the  arteries 
and  he  recounted  to  him  the  while  how  respiration 
among  animals  was  merely  a process  of  burning, 
accompanied  with  the  evolution  at  each  exhalation 
of  so  much  invisible  smoke  from  the  lungs — the  same 
smoke,  indeed,  as  comes  from  burning  charcoal: 
and  he  told  Humphry  that  he  would  one  day  come 
to  see  how  the  rotting  wood  underwent  precisely 
the  same  chemical  change  as  the  breathing  man,  and 
that  what  is  a process  of  death  and  decay  in  the  one 
is  a process  of  life  and  health  in  the  other. 

“ Indeed,”  concluded  the  old  gentleman,  “ there 
is,  perhaps,  no  sphere  of  knowledge  so  replete  with 
wonder  and  beauty  as  that  which  unfolds  to  us  the 
mysteries  of  our  own  existence — no  science  which 
gives  us  greater  wisdom  or  deeper  insight  into  the 
constitution  of  our  natures,  as  well  as  that  of  the 
elements  around  us.  To  comprehend  such  a sub- 
ject, even  vaguely,  requires  an  intimacy  with  al- 
most every  branch  of  learning,  dealing  as  it  does  at 
once  with  the  material  and  spiritual ; while  a just 
appreciation  of  the  wonders  it  reveals  cannot  fail  to 
inspire  us  with  the  highest  regard  for  life,  even  in 
its  rudest  forms,  and  render  us  more  keenly  alive 
to  suffering  than  the  rest  of  humanity,  from  the 


THE  FIRST  DRINK  AT  THE  WELL. 


87 


greater  sense  it  gives  us  of  the  causes  of  pain, 
while  it  arms  us,  at  the  same  time,  with  the  means 
of  relieving  anguish,  restoring  health,  and  often  of 
prolonging  existence. 

“ Some  there  are,”  he  added,  “ who  prefer  poetry 
to  philosophy  ; but  science,  Humphry,  rightly  under- 
stood, is  merely  the  translation  of  the  Great  Poem 
of  Nature — that  which  the  Almighty  himself  con- 
ceived when  he  designed  Creation.  There  may  be 
high  beauty  in  music,  boy ; but,  to  my  mind,  there 
is  even  higher  beauty  still  in  comprehending  the  phe- 
nomena by  which  the  Creator  has  fitted  us  to  enjoy 
it.  In  the  rich  glories  of  colour  there  is,  certainly, 
an  exquisite  feast  of  visual  delight ; but  what  array 
of  tints,  be  they  ever  so  beautifully  blended — what 
tracery  of  form,  be  it  ever  so  cunningly  put  to- 
gether— can  fill  the  mind  with  ecstasy  equal  to 
the  contemplation  of  that  splendid  little  translucent 
globe,  the  eye — a crystal  world  in  itself,  filled  with 
an  infinity  of  wonders — by  which  we  are  enabled  to 
perceive  the  light,  and  to  tell  one  hue  from  another  % 
What  work  of  art,  however  consummate  the  execu- 
tion— what  picture,  however  choice  the  painting  or 
grand  the  composition — what  architecture,  however 
commanding  the  mass  or  harmonious  the  details — 
and  what  poem,  even  though  the  verse  be  mellif- 
luent as  music  on  the  water,  though  the  imagery 
be  luminous  and  profuse  as  the  stars  in  winter,  and 
the  thoughts  subtle  as  the  mountain  air,  can  bear 


88 


THE  WONDERS  OF  SCIENCE. 


the  least  comparison,  either  as  regards  the  skill  of  its 
art,  the  craft  of  its  design,  or  the  nice  adjustment  of 
its  parts,  with  the  organism  of  the  smallest  animal- 
cule fashioned  by  the  Great  Artist,  Architect,  and 
Poet  of  All?’ 

The  sentence  was  barely  finished  when  the  sharp 
report  of  a gun  rattled  amidst  the  rocks,  and  Hum- 
phry, whose  eyes  had  been  turned  upward  as  he 
listened  to  the  wonders  recounted  by  the  doctor, 
saw  the  gull,  which  but  a moment  before  he  had 
noticed  almost  lying  on  the  air,  poised  on  its  white 
outstretched  wings,  bound  suddenly  upwards  with  a 
shriek,  and  the  instant  afterwards  it  tumbled  heavily 
on  the  crag  at  Mr.  Tonkin’s  side. 

The  old  gentleman  stretched  out  his  hand  and 
grasped  the  still  warm  and  quivering  form  of  the 
bird.  “ If  the  wings  of  this  body  had  been  moved 
by  some  piece  of  curious  mechanism,  Humphry,”  he 
said — “if  by  some  cunning  combination  of  cog- 
wheels, and  levers,  and  springs,  it  had  been  made  to 
beat  the  air  and  to  rise  by  clock-work  into  the  sky, 
how  would  men  have  prized  the  marvellous  appa- 
ratus ! Monarchs  would  have  given  immense  wealth 
to  possess  it : and  yet  the  machine  would  have  been, 
at  best,  but  a clumsy  toy  compared  with  the  exqui- 
site arrangement  here  ; for  in  this  wonderful  piece  of 
divine  mechanism  the  force  was  supplied  by  means 
of  little  threads  of  nerves  that  the  unaided  eye  can 
scarcely  trace — the  movement  given  by  muscles  so 


THE  FIRST  DRINK  AT  THE  WELL. 


89 


beautifully  elastic  that  no  artificial  fabric  can  imi- 
tate their  play — and  the  bones  jointed  together  so 
aptly,  that  when  our  wisest  engineers  wish  to  get 
movements  in  all  directions,  they  can  only  copy 
their  arrangement,  instead  of  designing  any  such 
hinges  for  themselves.  Then,  again,  to  give  light- 
ness to  the  whole,  these  same  bones  were  filled  with 
air,  and  the  living,  flying  machine,  so  made  more 
buoyant  in  the  thin  fluid  in  which  it  was  destined 
to  soar.  But  let  us  suppose,  Humphry,  that  it  might 
be  within  the  compass  of  art  to  reproduce  such  an 
apparatus  as  this  by  mechanical  means ; still  what 
mechanism,  however  skilful,  could  have  supplied  the 
wonderful  motive  power  that  lately  quickened  it? 
What  spring,  or  arrangement  of  weights,  could  imi- 
tate the  action  of  life  ? Could  steam  even,  or  electric- 
ity itself,  have  moved  the  wings  and  guided  them, 
like  the  subtle  principle  that  stirred  and  directed 
this  body  only  a few  moments  past  ? And  then,  what 
cunning  engineery  could  ever  have  performed  the 
function  of  the  senses?  Could  mechanism  have 
made  the  animal  see?  Could  the  galvanic  fluid- — - 
the  most  spiritual,  perhaps,  of  all  our  motive  powers 
— lfave  made  it  love  its  young,  or  know  when  to 
repair  its  strength  with  food  ? Ah ! had  the  thought- 
less fool  who,  for  wanton  sport,  Humphry— -who 
for  the  mere  sake  of  hitting  a moving  mark  in  the 
air — -known  and  pondered  over  all  this,  do  you 
not  think  he  would  have  found  more  pleasure 


90 


THE  WONDERS  OF  SCIENCE. 


in  watching  the  performance  of  all  its  wondrous 
functions  than  in  destroying  the  beautiful  principle 
which  animated  them  ? Had  he  needed  its  body  for 
food,  hunger  would  have  excused  him.  But  no ! It 
was  simply  the  petty  pleasure — the  little  spasm  of 
exultation — that  we  derive  from  success  in  trials  of 
skill  which  led  him  to  put  an  end  to  the  life  of  the 
poor  bird,  that  had  surely  as  much  divine  right  to 
its  place  in  creation  as  even  a king  himself.” 

Humphry  was  overjoyed  with  the  lesson  of  kind- 
ness and  wisdom  he  had  learnt.  He  had  been  so  en- 
raptured with  the  knowledge  that  Mr.  Tonkin  had 
poured  into  his  mind  that  he  sat  almost  like  one 
entranced,  with  his  spirit  lulled  in  a dream  of  bright 
things  he  had  never  heard  or  thought  of  before. 

The  boy  till  now  had  been  more  smitten  with  the 
beauty  of  creation  than  curious  as  to  its  mysteries. 
True,  in  his  romantic  visits  to  the  extremity  of  the 
island,  as  well  as  to  the  Mount  of  St.  Michael,  he 
had  been  often  led  to  wonder  how  the  huge  masses 
of  rock  had  come  there ; and  he  had  many  times 
pondered  over  the  origin  of  metals,  as  in  his  ram- 
bles he  had  passed  the  openings  of  the  mines  that 
perforated  the  surface  of  his  native  country,  wonder- 
ing as  he  went  along  why  a vein  of  one  ore  should 
be  deposited  here,  and  another  there.  As  he  no- 
ticed, too,  the  Atlantic  waves  lashing  the  Land’s 
End,  lie  would  repeatedly  question  himself  as  to 


THE  FIRST  BRINK  AT  THE  AVELL. 


91 


what  became  of  the  rocks  that  the  sea  was  for  ever 
crumbling  into  sand ; and  he  would  form  fanciful 
theories  in  his  own  mind,  as  to  how  the  detritus  of 
one  ancient  country  became  at  last  the  substratum 
of  some  new  one.  Again,  the  ebbing  and  flowing 
of  the  ocean  had  led  his  mind  to  ruminate  vaguely 
upon  the  mighty  pulsation  of  the  tides,  while  the 
sight  of  the  liquid  orb  of  the  sun  sinking  below 
the  ring  of  the  horizon,  away  towards  the  invisible 
shores  of  America,  had  often  turned  his  thoughts  to 
the  revolutions  of  the  planets,  and  set  him  rudely 
speculating  as  to  the  source  of  the  light  and  the  heat 
of  the  sun  itself. 

Still  the  youth  as  yet  had  found  more  pleasure 
in  contemplating  the  golden  glories  of  sunset,  than 
in  seeking  to  comprehend  the  wisdom  that  de- 
signed them.  The  sea,  too,  to  him  had  been  more 
an  object  of  grandeur  than  a stimulus  to  thought, 
Avhile  the  sight  of  the  rocks  had  filled  his  mind 
Avith  admiration  far  oftener  than  they  had  quick- 
ened it  with  inquiry.  The  mystery,  and  even  the 
beauty,  of  the  principle  of  life,  howe\~er,  had  never 
before  been  heeded  by  Humphry  ; so  that,  when  he 
heard  Mr.  Tonkin  relate  the  many  wonders  wrought 
in  the  changes  that  were  continually  going  on  in  his 
OAvn  frame,  the  boy  was  almost  overwhelmed  with 
the  flood  of  neAV  thoughts  that  poured  through  his 
brain,  and  he  felt  as  if  he  could  ha\Te  sat  and 
listened  to  the  old  man  the  long  night  through. 


92  THE  WONDERS  OF  SCIENCE. 

Accordingly,  when  Mr.  Tonkin  came  to  a con- 
clusion, Humphry  begged  him  to  proceed,  saying 
he  had  begotten  emotions  in  him  that  he  had  never 
known  before  ; and  he  felt  as  if  a burning  thirst  had 
come  upon  him  for  the  truth,  and  he  could  drink  of 
such  knowledge  for  ever  without  quenching  it. 

Mr.  Tonkin  was  pleased  to  find  he  had  stirred 
the  boy’s  thoughts  so  effectively ; and  he  promised 
him  that,  before  long,  he  would  place  him  in  a po- 
sition where  he  should  be  able  to  pursue  the  subject 
as  far  as  his  powers  could  carry  him. 

Not  many  weeks  after  the  above  conversation, 
Humphry,  to  his  exceeding  delight,  was  articled  to 
Mr.  Bingham  Borlase,  the  surgeon  and  apothecary 
of  Penzance  ; and  there,  alone  in  his  little  chamber, 
at  night,  he  wrote  the  following  passage  in  his  note- 
book : 

“ 1 have  neither  riches  nor  birth  to  recommend 
me  ; yet,  if  I live,  I trust  I shall  not  be  of  less 
service  to  mankind  and  to  my  friends  than  if  I had 
been  bom  with  these  advantages.”* 

* This  memorable  passage  was  written  in  a diary  kept  by 
Humphry  Davy  during  his  youth.  His  brother,  after  quoting  it, 
adds,  “-and  this  early  sentiment  never  forsook  him  ; even  in  his 
last  days  he  had  a feeling  of  the  same  kind,  looking  forward, 
were  his  life  spared,  to  greater  exertions.” 


) 


CHAPTER  Y. 

THE  FIRST  GLIMMER  OF  THE  SAFETY-LAMP. 

Humphry  was  hardly  at  home  in  his  new  quar- 
ters, when  an  incident  occurred  that  directed  his  mind 
towards  the  investigation  of  one  of  the  most  subtle 
and  mysterious  principles  in  nature. 

Mr.  Borlase  had  returned  from  his  day’s  rounds, 
and  as  he  was  busy  unfastening  the-  long  leggings 
that  covered  his  black  silk  stockings,  he  informed 
the  family,  who,  with  the  boy,  were  gathered  round 
the  tea-table  in  the  little  parlour  adjoining  the  shop, 
that  he  had  heard  that  day  of  a fearful  explosion 
which  had  occurred,  during  the  last  month,  in  one 
of  the  Welsh  coal-mines. 

u It  seems,”  said  the  doctor,  as  he  took  his  place 
at  the  table,  “ that  there  were  two  £ shifts,’  or  sets, 
of  men  employed  at  the  pit.  The  first  went  to  work 
at  four  in  the  morning,  and  were  relieved  by  the 
next  set  at  eleven  ; and  so  secure  was  the  mine  con- 
sidered— so  little  thought  of  danger,  indeed,  entered 
the  minds  of  the  pitmen — that  the  second  shift  of 


94 


THE  WONDERS  OE  SCIENCE. 


men  often  entered  the  mine  before  the  first  had 
left  it.  This  happened  to  be  the  case,  they  tell 
me,  at  the  time  of  the  accident ; for  shortly  after 
the  second  set  of  hands  had  descended  the  shaft, 
the  people  above-ground  were  alarmed  by  a terrible 
report,  followed  by  others  so  quickly,  that  it  sounded 
like  the  firing  of  infantry,  and  a sheet  of  flame  was 
seen  to  flash  from  the  mouth  of  one  of  the  shafts. 
The  ground  shook  as  if  with  an  earthquake,  the 
tremor  being  felt  for  half-a-mile  round  the  work- 
ings ; while  the  dull,  subterranean  boom  of  the  ex- 
plosion was  heard,  they  say,  nearly  four  miles  off. 
Vast  clouds  of  dust  rose  high  in  the  air,  in  the 
form  of  an  inverted  cone,  and  large  masses  of 
timber  and  fragments  of  coal  were  shot  straight 
up  from  the  pit-mouth,  as  from  a huge  piece  of 
artillery,  and  fell  with  a heavy  crash  near  it ; while 
the  dust,  borne  by  the  wind,  descended  in  a shower 
upwards  of  a mile  from  the  spot,  and  as  it  did  so,  it 
caused  a gloom,  I am  assured,  like  early  twilight,  in 
the  neighbouring  villages,  inhabited  chiefly  by  the 
families  of  the  miners. 

“ The  boom  was  no  sooner  heard,”  continued 
Mr.  Borlase,  u the  tremor  of  the  earth  felt,  and 
the  darkness  from  the  shower  of  ashes  perceived, 
than  the  wives  and  children  of  the  miners  rushed 
frantically  towards  the  pit.  Horror  and  dismay 
were  painted  on  every  face.  The  crowd  thickened 
from  all  sides,  so  that  in  a short  time  several  hun- 


THE  FIRST  GLIMMER  OF  TIIE  SAFETY-LAMP.  95 

dreds  of  women  and  children  were  gathered  round 
the  shaft.  The  air,  the  people  say,  resounded  with 
shrieks  and  cries  of  despair  for  the  fate  of  husbands, 
fathers,  and  sons,  from  many  a bursting  heart. 

“The  machinery,  it  was  then  found,  had  been 
rendered  useless  by  the  explosion,  so  that  it  was 
near  upon  an  hour  before  thirty-two  persons  — all 
that  survived  that  dreadful  catastrophe — had  been 
brought  to  daylight,  and  of  these  twenty-nine  only 
lived  to  relate  what  had  occurred  in  the  mine  be- 
low. 

“ It  was  now  discovered  that  one  hundred  and 
twenty-one,  men  and  boys,  had  been  in  the  pit  when 
the  accident  happened,  so  that  eighty -nine  poor  souls 
still  remained  entombed  in  the  workings.  Those 
who  had  their  friends  restored  to  them  appeared, 
it  is  said,  to  suffer  for  a while  as  much  from  an 
excess  of  joy  as  they  had,  a short  time  before,  from 
the  depth  of  despair ; while  those  who  were  yet  in 
the  agony  of  suspense  filled  the  air  with  shrieks 
and  howlings,  and  ran  about  wringing  their  hands 
and  throwing  their  bodies  into  the  most  frantic  and 
extravagant  gestures. 

“After  some  little  time,  it  appears  that  nine 
persons  volunteered  to  descend  into  the  pit,  with 
the  faint  hope  that  some  engulfed  below  might 
still  survive.  As  the  fire-damp,  however,  would 
have  been  instantly  ignited  by  candles,  those  who 
went  to  search  the  mine  lighted  their  way  by  4 steel- 


96 


THE  WONDERS  OF  SCIENCE. 


mills,’  as  they  are  called,  which,”  added  Mr.  Bor- 
lase,  turning  round  to  Humphry,  “are  small  ma- 
chines for  giving  light,  by  turning  a cylinder  of 
steel  against  a piece  of  flint ; for  it  has  been  found, 
I should  tell  you,  that  though  the  fire-damp  is  im- 
mediately ignited  by  flame,  it  is  not  explosible  by 
sparks.” 

The  remark  evidently  sank  deep  into  the  boy’s 
mind,  for  he  knit  his  brows  and  bit  his  lips  as  if  a 
sudden  thought  had  flashed  across  his  brain.  But 
Humphry  was  too  much  interested  in  the  narrative 
to  interrupt  the  doctor,  so  he  said  not  a word,  and 
waited  anxiously  for  Mr.  Borlase  to  proceed. 

“ The  men  who  had  descended  the  pit,”  continued 
that  gentleman,  “ attempted  to  make  their  way  to- 
wards the  spot  where  they  knew  the  miners  must 
have  been  at  the  time  when  the  explosion  happened. 
Their  progress,  however,  was  soon  intercepted  by 
the  prevalence  of  what  is  called  the  4 choke-damp’ 
— an  atmosphere  which  it  is  suffocation  to  inhale — 
and  the  sparks  from  the  steel-mill,  they  say,  fell  into 
this  like  dark  drops  of  blood. 

“ Deprived  of  light,  therefore,  and  nearly  stifled, 
they  were  forced  to  grope  their  way  back  to  the  shaft. 

“ As  each  came  up  he  was  surrounded  by  a group 
of  anxious  inquirers,  but  not  a ray  of  hope  could  be 
elicited.  It  was  impossible,  they  told  the  people, 
for  any  breathing  thing  to  live  in  the  mine.  At 
first,  the  assertion  seemed  to  obtain  some  credit, 


THE  FIRST  GRIMMER  OF  THE  SAFETY-LAMP.  97 

but  hope  still  lingered.  All  there  recollected  how 
persons  had  survived  similar  accidents,  and  stories 
were  told  how,  upon  opening  a mine  forty  days 
after  an  explosion,  men  had  been  found  still  alive, 
having  subsisted  during  the  time  on  horse-beans 
and  candle-ends.  Then  distrust  began  to  enter  the 
minds  of  the  crowd,  and  some  suggested  that  want 
of  courage  or  bribery  had  induced  the  men  who  had 
descended  to  magnify  the  danger ; so  that  when  it 
was  proposed  by  the  owners  to  close  the  mouth  of 
the  pit,  and  so  shut  out  the  air  from  it- — for  the  most 
experienced  ‘viewers’  had  pronounced  the  mine  to 
be  on  fire — the  proposition  was  received  with  cries 
of  4 Murder !’  and  with  expressions  of  determination 
to  oppose  such  a proceeding  with  violence ! 

“ All  that  night,  they  tell  me,”  the  doctor  proceed- 
ed, a many  of  the  widows  lingered  about  the  mouth 
of  the  pit,  with  the  hope  of  hearing  the  cries  of  a 
husband  or  a son. 

“The  next  morning  it  was  again  proposed  to 
exclude  the  air ; still  the  populace,  made  furious  by 
their  misery,  would  not  allow  the  project  to  be 
carried  out  until  some  others  had  again  descended 
the  shaft.  But  none  could  now  be  found  hardy 
enough  to  enter  the  jaws  of  the  burning  cavern. 
At  length,  however,  two  brave  fellows  were  induced 
to  make  the  perilous  attempt,  and  they  nearly  lost 
their  lives  in  so  doing. 

“ The  account  given  by  these  adventurers  (for 

G 


98 


THE  WONDERS  OF  SCIENCE, 


they  confirmed  the  opinion  as  to  the  pit  being  on 
fire)  ultimately  convinced  the  people  of  the  impos- 
sibility of  their  friends  surviving  in  so  deadly  an 
atmosphere,  and  reconciled  them  to  the  plan  of  ex- 
cluding the  air.  Accordingly  the  shaft  was  closed, 
with  the  eighty-nine  poor  souls  entombed  in  it,  and 
more  than  a month  elapsed  before  the  mine  was 
opened  again  and  in  a state  to  admit  of  an  examin- 
ation. 

“ During  this  interval,  I leave  you  to  imagine,” 
went  on  the  apothecary,  “ what  must  have  been  the 
terrible  suspense  of  those  whose  love  made  it  impos- 
sible to  eradicate  all  hope  from  their  bosoms.  The 
widows,  anxious  to  believe  that  their  husbands  still 
lived  in  the  closed  mine,  gave  a ready  credence  to 
the  idle  tales  of  escape  that  were  continually  being 
circulated  through  the  country.  These  inventions, 
however,  had  the  effect  of  daily  harrowing  up  afresh 
the  sorrows  of  the  people ; so  that  when  the  morn- 
ing came  that  had  been  appointed  for  the  re-opening 
of  the  pit,  the  distress  of  the  neighbourhood  burst 
forth  once  more  with  almost  redoubled  fury. 

“ A great  concourse  of  people  assembled  round  the 
mine  on  that  sad  day  : some  came  out  of  curiosity, 
others  out  of  public  sympathy,  but  the  greater  part 
came  there  with  broken  hearts  and  streaming  eyes, 
intent  on  once  more  beholding  the  loved  form  of  a 
father,  brother,  husband,  or  son. 

“ Soon  a message  was  despatched  for  a number 


THE  EIliST  GLIMMER  OE  THE  SAFETY-LAMP.  90 

of  coffins  to  be  in  readiness  at  the  pit-mouth.  Up- 
wards  of  eighty  of  these  had  been  ready  prepared., 
and  they  had  to  pass  by  the  miners’  villages  on  their 
way  to  the  shaft.  As  soon  as  a cart-load  of  them 
was  seen,  the  howling  of  the  women,  who  had  not 
yet  found  their  way  to  the  melancholy  spot,  floated 
on  the  breeze  in  low,  fitful  gusts,  presaging  a scene 
of  the  greatest  distraction  and  confusion  ; and  as 
each  load  of  coffins  came  to  the  pit,  it  brought  a long 
train  of  wretched  mourners  in  its  wake. 

“ The  bodies  of  the  ill-fated  men  were  found 
under  various  circumstances.  One,  from  his  posi- 
tion, must  have  been  asleep  when  the  explosion 
happened ; others  were  huddled  together  in  ghastly 
confusion — twenty-one  were  found  in  a heap  in  one 
spot.  The  power  of  fire  was  visible  upon  all : 
some  were  scorched;  others  almost  torn  to  pieces; 
while  others,  again,  appeared  as  if  they  had  been 
stifled  at  their  work. 

“ Then  came  the  heart-rending  scene,”  added  Mr. 
Borlase,  “ of  mothers  and  widows  examining  the 
mangled  remains  for  marks  by  which  to  identify  the 
bodies  of  their  lost  sons  and  husbands.  Few,  how- 
ever, were  able  to  recognise  their  relatives  by  their 
features  ; their  clothes,  their  shoes,  and — when  these 
were  too  much  burnt  to  be  known  again — their  to- 
bacco-boxes, or  some  token  of  affection,  were  often 
the  only  indications  by  which  the  lost  friend  could 
be  singled  out  from  the  rest. 


100 


THE  WONDERS  OF  SCIENCE. 


“ Every  family  had  made  some  arrangements  for 
receiving  the  dead  bodies  of  their  kindred,  but  the 
doctor  had  very  properly  stated  that,  in  his  opin- 
ion, such  a proceeding  might  spread  a putrid  fe- 
ver through  the  neighbourhood,  and  the  first  body, 
when  exposed  to  observation,  presented  so  horrible 
and  corrupt  an  appearance,  that  the  people  were 
induced  to  consent  that  each  corpse  should  be  in- 
terred as  soon  as  it  was  discovered — on  condition 
that  the  hearse,  in  its  way  to  the  chapel-yard, 
should  pass  by  the  door  of  the  deceased. 

44  And  the  condition  was  duly  complied  with,” 
concluded  the  doctor,  solemnly.  44  Hour  after  hour, 
and  day  after  day — for  the  finding  and  removal  of 
the  bodies  continued  for  upwards  of  a week — the 
funeral  carriage  might  be  seen  slowly  wending  its 
way  through  the  half  - desolate  miners’  villages, 
passing  first  by  the  door  of  one  closed  cottage, 
and  then  by  another,  while  at  the  hatches  of  the 
others  stood  groups  of  women,  the  greater  part  of 
whom  were  habited  in  black,  with  little  things  by 
their  side,  and  some  with  infants  in  their  arms, 
mostly  wearing  some  humble  mark  of  mourning. 
As  the  hearse  moved  on,  the  women,  with  tears  in 
their  eyes,  would  tell  one  another  whose  body  was 
then  on  its  way  to  its  last  home,  and  each  would 
have  some  little  story  to  recite  of  good  done  and 
charity  bestowed  by  the  ill-fated  man,  while  all 
would  sigh  to  think  what  would  become  of  the 


THE  FIRST  GLIMMER  OF  THE  SAFETY-LAMP.  101 

wretched  widows  and  little  orphans  who,  as  the 
bier  stopped  at  the  cottage,  might  be  seen,  with 
streaming  eyes  and  dejected  heads,  to  issue  forth  and 
follow  the  funeral  carriage  slowly  and  sadly  to  the 
grave. 

“ For  ten  long,  melancholy  days,”  said  Mr.  Bor- 
lase,  mournfully,  “ were  the  shutters  of  the  houses 
closed  in  the  miners’  villages,  and  for  ten  days  did 
the  bell  of  the  neighbouring  chapel  continually  toll 
- — for  the  finding  of  the  bodies  lasted  all  this  time: 
and  by  this  one  terrible  accident  there  were  no  less 
than  ninety-two  pitmen  hurled  into  eternity,  while 
as  many  as  forty  widows  and  one  hundred  and  six 
orphan  children  were  deprived  of  their  protectors 
and  ordinary  means  of  subsistence.”* 

Mr.  Borlase,  on  finishing  his  melancholy  story, 
turned  to  Humphry,  and  saw  the  tears  trickling 
from  his  cheeks. 

There  was  a silence  among  all  present,  as  if  the 
awe  of  the  calamity  was  still  pressing  on  their 
hearts. 

Presently  the  impulsive  boy  started  to  his  feet 

* The  details  of  this  accident  are  taken  from  the  account  of  an 
explosion  which  occurred  at  Felling  Colliery,  near  Sunderland, 
on  the  12th  of  May,  1812,  and  of  which  a narrative  was  prefixed 
by  the  Rev.  John  Hodgson  to  the  published  form  of  the  funeral 
sermon  he  preached  on  the  occasion.  It  was  this  fearful  explo- 
sion which  led  to  the  formation  of  the  Society  for  the  Prevention 
of  Accidents  in  Coal  Mines;  and  it  was  at  the  request  of  the 
members  of  this  body  that  Humphry  Davy  was  induced  to  per- 
fect his  safety-lamp. 


1 02  THE  WONDERS  GE  SCIENCE, 

and  cried,  “ I’ll  put  an  end  to  this  shocking  misery, 
please  God  I will,  some  day.” 

The  quick  eye  of  young  Humphry  saw  a smile 
play  faintly  on  the  doctor’s  lip,  and  he  added,  “ I 
know,  sir,  you  have  reason  to  doubt  my  power  to 
do  as  I say,  and,  perhaps,  it  may  take  me  years  of 
hard  study  to  gain  the  knowledge  to  enable  me  to 
compass  my  end  ; but  though  it  cost  me  a lifetime 
I will  master  it  at  last.  I have  sufficient  faith 
in  the  goodness  of  the  Creator,  to  believe  that  these 
terrible  afflictions  come  upon  us  only  through  our 
ignorance,  and  that  if  we  but  study  His  will,  as 
expressed  in  the  laws  of  the  universe  in  which  He 
has  placed  us,  He  has  given  us  the  faculty  to  avert 
misery,  and  to  turn  the  current  of  Nature  to  our  own 
welfare  rather  than  injury.” 

Mrs.  Foxell  (Mr.  Borlase’s  sister),  who  was  pre- 
siding at  the  tea-table,  and  who  had  already  learnt 
to  esteem  Humphry  highly  for  the  generous  qualities 
of  his  nature,  was  moved  almost  to  tears  with  the 
benevolent  impulses  of  the  boy  ; for  she  was  natu- 
rally of  a kindly  disposition,  and  the  melancholy 
details  of  the  accident  had  so  affected  her,  that 
when  she  heard  the  youth  vow  he  would  one  day 
put  an  end  to  such  calamities,  the  transport  of 
joy  she  felt  was  too  much  for  her  woman’s  heart, 
and  though  she  would  have  cheered  him  on,  there 
was  an  hysteric  spasm  in  her  throat  that  prevented 
her  utterance  for  a time. 


the  first  glimmer  of  the  safety-lamp.  103 

Presently  the  lady  said,  “ Do  not  be  discouraged 
by  what  my  brother  may  say  to  you,  Humphry. 
He  has  lived  too  long  in  the  world  to  be  as  hope- 
ful as  you  are,  and  he  is  so  accustomed  to  scenes  of 
anguish  that  suffering  is,  with  him,  almost  an  every- 
day occurrence.  But  you  and  I,  boy,  are,  thank 
Heaven,  unused  to  such  sights,  so  that  the  mere 
recital  of  them  stirs  us  to  the  depths  of  our  natures. 
Besides,  it  is  only  a woman  who  can  fully  compre- 
hend the  distress  wrought  by  such  a catastrophe  as 
my  brother  has  recounted  to  us ; for  the  real  suffer- 
ing in  all  such  cases  falls  lighter  on  those  who  are 
even  destroyed  by  it  than  it  does  upon  those  who 
are  left  behind.  It  is  not  so  much  the  dead  hus- 
bands I grieve  for  as  the  living  widows ; the  lost 
fathers  felt  but  a momentary  pang,  but  the  fatherless 
children  have  years  of  misery  to  pass  through : and 
it  is  because  my  sex  teaches  me  to  understand  these 
things  deeper  than  yours,  that  I,  for  the  sake  of  the 
poor  living  victims — the  wives  and  babes,  beggared 
in  heart  as  well  as  in  means — would  not  have  a 
word  said  that  would  take  away  one  spark  of  hope 
from  your  noble  purpose.  Though  the  prospect  of 
success  may  appear  barren  to  some  minds,  neverthe- 
less if  you,  Humphry,  can,  in  the  ardour  of  your 
sympathy,  imagine  such  an  object  to  be  barely  pos- 
sible of  attainment,  I say  to  you,  Go  on ; and  God 
speed  you  in  your  good  work.  You  wish  such  a 
result  to  be  possible,  and  therefore  believe  it  to  be  so, 


104 


THE  WONDERS  OF  SCIENCE, 


and  believing  it,  perhaps  you  may  find  it  to  be  as  you 
fancy ; whereas  if  you  had  no  faith  in  it  you  would 
never  work  at  it,  and  consequently  could  never  ac- 
complish it.  Think,  too,  if  you  should  one  day  gain 
your  end,  what  honour  would  await  you- — how  many 
thousand  poor  creatures  would  hail  you  as  their  pre- 
server— what  evils  you  would  be  the  means  of  pre- 
venting—-ay,  and  even  what  wealth  you  might  reap 
from  such  a discovery,  for  you  could  secure  it  to  your- 
self, and  so  derive  a large  income  from  the  profits  of 
it.” 

“No,  my  good  madam,”  replied  Humphry,  half 
indignant  at  the  idea  of  enriching  himself  by  such 
means,  “ I would  never  think  of  such  a thing.  My 
sole  object  would  be  to  serve  the  cause  of  humanity, 
and,  if  I succeeded,  I should  be  amply  rewarded  in 
the  gratifying  reflection  of  having  done  so.  All  I 
desire  is  a competence,  and  this,  I hope,  my  pro- 
fession will  yield  me ; more  wealth  might  be  troub- 
lesome, and  distract  my  attention  from  pursuits  in 
which,  even  now,  I delight.  Riches,”  he  added, 
“ could  not  give  me  either  fame  or  happiness ; they 
might,  undoubtedly,  enable  me  to  put  four  horses  to 
my  carriage,  but  what  would  it  avail  me  to  have  it 
said  that  Humphry  Davy  drives  his  carriage  and 
four?”* 

* The  above  generous  sentiments  are  taken,  almost  verbatim, 
from  a letter  of  Mr.  Buddie — “ a person,”  says  the  biographer  of 
our  hero,  “ whose  extensive  practical  knowledge  justly  entitled 
him  to  be  considered  as  the  highest  authority  on  all  subjects  con- 


THE  FIRST  GLIMMER  OF  THE  SAFETY-LAMP.  105 


The  noble  disinterestedness  of  these  sentiments 
produced  a deep  impression  upon  all  present,  for  they 
were  uttered,  not  in  the  same  passionate  tone  as  that 
in  which  the  boy  had  previously  spoken,  but  calmly 
and  almost  gravely,  as  if  they  were  the  result  of  long 
reflection,  and  showed  that  the  youth  had  already 
learnt  to  prize  fame  more  than  wealth — that  his 
mind  was  bent  on  winning  an  honourable  reputation 
rather  than  amassing  a worldly  fortune. 

Old  Mr.  Borlase,  the  venerable  father  of  Hum- 
phry’s master,  looked  with  wonder  and  admiration 
at  the  youth,  and  drawing  him  closely  to  him,  ex- 
claimed, “ There’s  a brave  lad ! Yon  remind  me, 

nected  with  the  art  of  mining,”  and  who  was  of  great  service  to 
Davy  in  carrying  out  his  invention  of  the  safety-lamp.  That 
gentleman,  writing  to  Dr.  Paris,  says,  “ Sir  Humphry  Davy  ac- 
companied me  into  some  of  our  fiery  mines,  to  prove  the  efficacy 
of  his  lamp.  Nothing  could  be  more  gratifying  than  the  result 
of  the  experiments,  as  they  inspired  everybody  with  perfect  con- 
fidence in  the  security  which  his  invention  had  afforded.  Sir 
Humphry  was  delighted,  and  I was  overpowered  with  feelings  of 
gratitude  to  the  great  genius  which  had  produced  it.  I felt,  how- 
ever,” continues  Mr.  Buddie,  “that  he  did  not  contemplate  any 
pecuniary  reward,  and  in  a private  conversation  I remonstrated 
wfith  him  on  the  subject.  I said,  ‘You  might  as  well  have  secured 
this  invention  by  a patent,  and  received  your  five  or  ten  thousand 
a-year  for  it.’  The  reply  of  this  great  and  noble-minded  man  was, 
‘No,  my  good  friend,  I never  thought  of  such  a thing,’”  etc.  as 
above  given.  “I  expostulated,”  adds  Mr.  Buddie,  “saying, 
that  his  ideas  were  much  too  philosophic  and  refined  for  the  occa- 
sion. He  replied,  ‘ I have  enough  for  all  my  views  and  purposes  ; 
more  wealth  might  be  troublesome,”’  and  so  on,  the  remainder 
of  the  speech  being  nearly  word  for  word  with  that  which  young 
Humphry  has  been  here  made  to  deliver. 


106 


THE  WONDERS  OF  SCIENCE. 


Humphry,  of  my  poor  brother  the  clergyman,  who 
Is  dead  and  gone  now,  rest  his  soul ! — I mean  him, 
you  know,  that  wrote  the  ‘ History  of  Cornwall 
a wonderful  book  it  is,  too  ! — he’d  just  the  same  no- 
tions when  he  was  a youngster,  and  used  to  say 
that  money  was  only  of  value  for  the  happiness  it 
could  bring,  and  that  there  was  more  real  pleasure 
to  be  found  in  seeking  and  discovering  the  truth 
than  the  richest  fortune  could  purchase.  I am 
sure,  for  my  part,  lad,  I hope  you  may  succeed  in 
your  noble  object ; and  I have  seen  quite  enough 
changes  in  my  time  to  think  nothing  impossible 
now.  Why,  I have  heard  my  grandfather  say  that, 
when  he  was  a boy,  coal  itself  was  seldom  used  as 
fuel,  and  now  see  what  wonders  are  being  worked 
by  it.  Haven’t  we  just  had  one  of  those  wonderful 
steam-engines,  which  have  been  of  late  years  invent- 
ed by  Mr.  Watt,  put  up  at  the  Wherry  Mine  close 
by?”* 

The  boy  nodded  quickly,  as  if  he  was  well  ac- 
quainted with  the  locality. 

“ And  there,”  continued  the  old  gentleman,  “ that 
great  monster  of  brass  and  iron  goes  on,  day  after  day 

* Watt’s  first  patent  was  in  the  year  1769,  and  that  for  his 
double  engine  was  in  1781.  Dr.  Davy,  in  speaking  of  the  Wherry 
Mine  as  being  a place  of  favourite  resort  with  his  brother  during 
his  youth,  says,  “The  steam-engine  there  (an  invention,”  he 
adds,  “ which  had  only  a short  time  before  been  perfected  by 
Mr.  Watt)  was  one  of  the  earliest  that  had  been  introduced  into 
Cornwall.” 


THE  FIRST  GLIMMER  OF  THE  SAFETY-LAMP.  107 

and  night  after  night  (though  the  shaft  of  the  mine, 
you  know,  is  in  the  sea,  and  the  workings  entirely 
underneath  the  sands),  acting  at  a distance  over  the 
surface  of  the  ocean,  and  drawing  up  the  water  from 
beneath  its  bed ; and  all,  too,  by  means  of  a few 
bushels  of  coals.  I am  sure  when  I first  saw  the 
engine  lifting  up  its  arms,  and  snorting  away  as  if 
with  the  heavy  labour  it  was  doing,  it  put  me  in 
mind  of  the  old  fable,  I learnt  at  school,  of  Prome- 
theus, who  stole  fire  from  the  sun,  you  know,  boy, 
and  made  men  with  it  out  of  the  materials  of  the 
earth.  For  it  struck  me  as  being  a huge  steam  man 
— a kind  of  monster  labourer,  as  it  were,  that  would 
work  on  for  ever,  without  needing  any  sleep,  and 
without  knowing  any  fatigue  ; and  that  wanted  only 
coals,  instead  of  bread  and  meat,  to  keep  it  going. 
Ah ! we  live  in  wonderful  times,  my  lad,  that  we 
do ; and  whatever  the  world  will  come  to  in  a few 
years,  when  I am  dead  and  gone,  is  more  than  I can 
say.  Why,  Mrs.  Foxell  here  was  reading  to  me  the 
other  day,  out  of  the  ‘ Sherbourne  Mercury,’  a para- 
graph, saying,  that  a Mr. — Mr. — What  was  the 
name,  my  dear?” 

“ Symington,”  answered  the  lady  appealed  to. 

“ Yes  ; that’s  it ! — Mr.  Symington,”  proceeded 
the  old  gentleman,  “ had  been  making  some  experi- 
ments on  the  Clyde  to  propel  a vessel,  without  sails 
or  oars,  over  the  water — what  do  you  think  of  that  ? 
— and  that  he  had  actually  got  a large  boat  to  move 


108 


THE  WONDERS  OF  SCIENCE. 


some  three  or  four  miles  an  hour  by  means  of  paddles 
worked  by  a steam-engine  on  board  the  vessel.* 
Dear,  dear  ! What  shall  we  come  to  next,  I wonder ! 
They  say  in  the  paper,  too,  that  the  experiment  was 
perfectly  successful;  so  that,  I dare  say,  in  a few 
years  our  sailors  will  be  no  longer  at  the  mercy  of  the 
winds,  and  if  they  have  only  a stock  of  coals  aboard, 
they’ll  be  able  to  traverse  the  seas  which  way  they 
like.  Ah ! coal  is  a wonderful  thing,  that  it  is, 
Humphry.  But  I’m  afraid  that  when  we  sit  and 
warm  ourselves  by  the  fire,  we  seldom  give  heed  to 
the  dangers  and  hardships  suffered  by  the  poor  creat- 
ures who  are  far  away  under-ground,  digging  it  out 
of  the  bowels  of  the  earth  for  us.” 

u That’s  true  enough,”  interposed  the  doctor, 
“and  it’s  long  been  an  opinion  of  mine  that  the 
greatness  of  England  will  soon  depend,  not  so  much 
on  the  energy  of  its  people  as  the  extent  of  its  coal- 
fields. You  have  heard,  doubtlessly,  that  Mr.  Mur- 
doch, in  our  own  county  here,  has,  within  the  last 
year  or  two,  made  a successful  application  of  the 

* W.  Symington  (according  to  Haydn’s  Dictionary)  made  a 
passage  on  the  Forth  and  Clyde  Canal  in  1789.  In  1807,  Fulton 
started  a steam-boat  in  America,  on  the  river  Hudson.  In  1812, 
steam-vessels  first  began  plying  on  the  Clyde  ; but  it  was  not  till 
the  year  1815  that  the  first  steam-vessel  made  its  appearance  on 
the  Thames.  This  was  a boat  from  Glasgow  ; for  it  was  only  in 
that  year  the  first  steamer  was  built  in  England.  Ten  years  after- 
ward (1825)  Captain  Johnston  received  <£10,000  for  making  the 
first  steam  voyage  to  India  in  the  Enterprise.  In  the  year  1852 
there  were  1227  steam-vessels  belonging  to  the  United  Kingdom. 


THE  FIRST  GLIMMER  OF  THE  SAFETY -LAMP.  109 

gas  from  coal  to  the  purposes  of  illumination ; he 
has  produced  by  it  a light  much  more  brilliant  than 
that  of  any  lamp,  and  which  requires  no  feeding  nor 
trimming,  nor  has  it  any  wick;  and  I am  told  that 
he  speaks  confidently  of  its  being  possible  to  light 
our  streets  and  houses  by  such  means.*  But  I must 
confess,  that  I myself  can  hardly  go  with  the  gentle- 
man so  far  as  that.” 

“Well,  for  my  part,  Bingham,”  interrupted  the 
father,  “ I am  ready  to  believe  anything.  I have 
lived  to  see  mail-coaches  introduced  throughout  the 
country  for  expediting  the  post,  and  letters  that 
used  to  take  near  upon  a fortnight  to  go  from  here 
to  London,  now  carried  the  same  distance  in  little 
more  than  two  days.j  So  nothing  they  could  do 

* Gas  was  first  evolved  from  coal  by  Clayton,  in  1739.  Its 
application  to  the  purposes  of  illumination  was  first  tried  by  Mr. 
Murdoch,  in  Cornwall,  in  1792.  Ten  years  after  this  (in  1802) 
Bolton  and  Watt’s  foundry,  at  Birmingham,  exhibited  the  first 
display  of  gas-lights  during  the  rejoicings  for  peace.  The  first 
manufactory  permanently  lighted  by  gas  was  a cotton  mill  at 
Manchester — this  was  in  1805.  Gas  was  first  used  for  lighting 
Pall  Mall,  in  London,  in  1809,  and  in  1814  it  had  become  general 
throughout  the  metropolis.  The  gas-pipes  in  and  round  London 
are  now  said  to  be  more  than  1100  miles  in  length. 

f Mail-coaches  were  first  set  up  at  Bristol,  Aug.  2,  1784,  and 
at  the  end  of  1785  they  became  general  in  England.  This  plan 
for  the  conveyance  of  letters  was  the  invention  of  Mr.  Palmer, 
at  Bath.  The  mails  had  previously  been  conveyed  by  carts 
with  a single  horse,  or  by  boys  on  horseback.  From  the  estab- 
lishment of  mail-coaches  the  prosperity  of  the  Post-office  com- 
menced. The  year  before  their  introduction  the  postal  revenue 
was  only  £146,000,  and  it  ultimately  increased  to  £2,500,000. 


110 


THE  WONDERS  OF  SCIENCE. 


would  astonish  me  after  that ! No,  not  even  if  I 
was  to  hear  that  the  mail-coaches  themselves  were 
driven  by  coals,  and  at  twice  the  rate  they  go  at 
now.” 

This  was  considered  so  wonderful  a stretch  of  im- 
agination on  the  part  of  the  old  gentleman,  that  the 
whole  company  laughed  heartily  at  the  apparent  im- 
possibility of  such  an  achievement. 

“You  may  smile,”  went  on  the  old  man,  “but 
steam  is  only  in  its  infancy  yet,  depend  upon  it; 
and  the  engineer  at  the  Wherry  Mine,  when  I 
was  talking  to  him  about  the  machine  there,  told 
me  that  there  was  force  enough  in  a bushel,  or 
eighty-four  pounds  of  coals,  when  properly  con- 
sumed, to  raise  70,000,000  pounds  weight  one  foot 
high.  Now,  the  ascent  of  Mont  Blanc,  from  the 
valley  of  Chamouni,  is  said  by  travellers  to  be 
the  most  toilsome  feat  that  a strong  man  can 
execute  in  two  days;  nevertheless,  I find  by  cal- 
culation” (and  the  old  gentleman  drew  a bit  of 
paper  from  his  waistcoat  pocket)  “that  the  com- 
bustion of  only  two  pounds  of  coal  would  be  suffi- 
cient, by  means  of  a steam-engine,  to  lift  a man  to 
the  summit.  Again,  the  great  Pyramid  of  Egypt 
is  composed  entirely  of  granite,  it  stands  on  eleven 
acres  of  ground,  and  is  500  feet  high,  so  that 
its  entire  weight  has  been  calculated  to  be  about 
13,000  million  pounds;  consequently  about  180 
bushels  of  coal  would  be  sufficient  to  raise  the 


THE  FIRST  GLIMMER  OF  THE  SAFETY-LAMP.  Ill 

entire  mass  twelve  inches  from  its  base.*  So  that 
you  see,  Humphry,  what  a wonderful  thing  coal  is, 
and  the  large  amount  of  force  that  lies  locked  up  in 
every  pound  of  it.” 

“I  do,  sir,”  said  the  boy,  “and  it  is  this  which 
makes  me  wish  to  decrease  the  suffering  attendant 
upon  the  working  of  so  valuable  a mineral.  The 
account  of  the  accident  which  Dr.  Borlace  has  just 
told  us,  has  so  harrowed  my  feelings,  that  I shall 
spare  neither  time  nor  labour  in  seeking  to  discover 
the  causes  upon  which  such  calamities  depend,  so 
as  to  find  out  the  means  by  which  to  prevent  them 
for  the  future.  It  may  be  some  years  before  I shall 
be  able  to  perfect  my  plans,  but  perfected  they  shall 
be  one  day  if  my  life  be  spared ; and  then  I have 
no  fear  that  a discovery,  having  for  its  object  the 
preservation  of  human  life  and  the  diminution  of 
human  misery,  will  be  either  neglected  or  forgot- 
ten. However  high  the  gratification  of  possessing 
the  good  opinion  of  society,  there  is  a still  more 
exalting  pleasure  in  the  consciousness  of  having  la- 
boured to  be  useful.”! 

* See  Sir  John  Herschel’s  “Introduction  to  the  Study  of 
Natural  Philosophy.” 

f These  are  Davy’s  own  words,  being  the  concluding  passage 
of  his  work  “ On  the  Safety-Lamp.” 


CHAPTER  VI. 


THE  WONDERS  OF  HEAT:  ITS  SOURCES. 

Humphry  was  so  full  of  his  project,  that  all  the 
day  long  he  could  think  of  little  else,  and  at  night 
he  lay  awake  in  his  bed  for  many  hours,  planning 
an  infinity  of  rude  schemes  for  accomplishing  the  ob- 
ject he  had  in  view.  He  devised  and  fashioned  a 
number  of  odd  contrivances,  too,  for  the  purpose,  but 
each  in  its  turn  was  found  to  be  of  little  or  no  avail. 

Nevertheless,  the  idea  was  too  great  to  be  hastily 
abandoned,  and  the  sense  of  the  fame  that  success 
in  such  an  undertaking  would  assuredly  give  to  his 
name  had  entered  so  deep  into  the  boy’s  mind,  that 
he  got  to  crave  more  and  more  for  worldly  honours ; 
and  he  would  sit  of  an  evening,  alone  among  the 
rocks,  dreaming  of  the  time  when  he,  a poor  Corn- 
ish boy,  was  to  be  ranked  among  the  intellectually 
noble,  and  reverenced  throughout  Europe  for  his 
genius  and  his  benevolence. 

Nor  did  the  lad  fail,  when  he  visited  his  mother, 
to  confide  to  her  all  his  hopes  of  success  and  renown ; 
and  when  the  widow  heard  that  he  was  bent  on  dis- 


THE  WONDERS  OE  HEAT. 


113 


covering  the  means  of  saving  the  lives  of  the  poor 
miners — a class  whom  she  had  long  learnt  to  pity, 
for  she  had  been  brought  ”p  in  the  midst  of  them, 
as  it  were — she  felt  prouder  than  ever  of  her  dar- 
ling boy,  and  shed  many  a tear  of  joy  over  him. 

Mrs.  Foxell,  too,  when  she  beheld  Humphry’s  vex- 
ation at  the  repeated  failures  of  the  models  he  con- 
structed, encouraged  the  lad  in  every  way,  remind- 
ing him  that  he  himself  had  said  the  project  would 
cost  him  years  of  hard  study  to  accomplish. 

Accordingly,  after  many  disappointments,  Hum- 
phry himself  began  to  see  that  he  could  only  hope 
to  attain  the  result  he  desired  by  making  himself 
acquainted  with  all  that  was  already  known  upon 
the  matter.  He  was  ignorant  even  of  the  laws  of 
combustion  in  general,  and  the  rude  experiments  he 
had  made  had  set  his  mind  craving  for  knowledge 
on  the  subject.  “Why  did  this  thing  burn,  and 
that  not?”  he  would  inwardly  inquire.  “How 
came  it  that  one  body,  as  gunpowder  for  example, 
went  alight  all  of  an  instant,  and  another,  like  tin- 
der, took  a long  time  to  smoulder  away?  And 
why  was  phosphorous  so  easy  to  kindle,  and  wood, 
comparatively,  so  difficult,  that  the  slightest  friction 
would  inflame  the  one,  whereas  it  required  a long 
time  to  light  the  other  by  such  means  ? What 
mysterious  process,”  he  would  ask  himself,  “went 
on  when  any  substance  burst  into  flame,  and  whence 

came  the  light  and  heat  that  were  then  given  out 

it 


114  THE  AVONDEJIS  OF  SCIENCE, 

from  materials  that,  a few  moments  before,  had  been 
dark  and  cold  ? Could  the  light  and  heat  have  been 
imprisoned  in  the  substance,  and  Avere  they  set  free 
during  the  combustion;  or  were  these  powers  gen- 
erated merely  by  the  burning  of  the  bodies'?” 

Then  Humphry’s  mind  darted  off  to  the  deeper 
question,  “ What  Avere  the  principles  of  light  and 
heat  themselves  % Were  they  one  and  the  same,  or 
two  distinct  powers  in  nature?  In  a winter’s  day,” 
he  mused,  “ we  have  the  same  light  from  the  sun, 
and  but  little  heat ; Avhilst  in  all  cases  of  artificial 
illumination  there  is  great  heat  and  but  little  light, 
compared  with  that  of  the  solar  rays.” 

These  and  many  other  such  puzzling  inquiries 
passed  through  Humphry’s  brain,  and  left  his  mind 
in  such  a state  of  perplexity  that  he  could  not  rest 
without  a clearer  insight  into  the  subject.  He  soon 
saAV,  too,  how  silly  he  had  been  in  setting  to  work 
before  he  had  availed  himself  of  the  discoveries  of 
those  who  had  gone  before  him ; for,  he  would  say, 
Iioav  could  he  think  of  finding  out,  by  himself,  all 
that  was  known  of  the  science  of  heat  and  light, 
Avhen  each  of  those  sciences,  as  Mr.  Tonkin  had  told 
him,  had  taken  thousands  of  the  wisest  minds — ay, 
and  thousands  of  years  of  intense  study — to  build 
up  ; for  in  them  Avas  contained  the  accumulated  ex- 
perience of  all  mankind  from  all  time.  Yet,  because 
the  truths  were  free  to  the  Avorld,  he  had  refused  to 
avail  himself  of  them,  and,  like  a proud  fool,  had 


THE  WONDERS  OF  HEAT. 


115 


though  he  could  compass  his  end  without  any  such 
knowledge  at  all. 

It  was  not  long  before  Humphry  was  hard  at 
work  making  himself  master  of  the  laws  of  heat. 
He  had  borrowed  of  Mr.  Tonkin  the  best  book  then 
extant  upon  the  subject,  and  often  when  the  streets 
of  the  little  town  in  which  he  lived  were  silent  as 
the  tomb — and  the  distant  bell  of  Madern  Church, 
as  it  tolled  the  morning  hours,  was  heard  to  boom 
upon  the  still  air,  almost  like  a moan — and  the  sound 
of  the  waves  that  rippled  upon  the  neighbouring 
shore  stole  on  the  ear  softly  as  the  murmur  of  a 
sea-shell — the  candle  might  be  seen  burning  in  the 
boy’s  chamber,  making  the  little  diamond  panes  of 
the  casement  shine  like  plates  of  amber  in  the  dark- 
ness (for  every  other  window  in  the  street  looked 
black  from  the  want  of  light),  while  the  observant 
eye  could  trace  on  the  white  wall  on  one  side  of  the 
room,  the  huge  distorted  shadow  of  the  lad  bending 
over  his  books. 

As  Humphry  read  on,  and  got  to  see  clearer  and 
deeper  into  the  nature  and  properties  of  the  subtle 
principle  he  was  studying,  he  grew  more  and  more 
enraptured  with  the  wonders  and  the  knowledge 
that  were  opened  up  to  him  at  every  step  ; and  often 
when  some  new  discovery  burst  upon  his  mind  he 
would,  in  the  fervour  of  his  admiration,  fall  upon 
his  knees,  there  alone  in  his  chamber  at  night-time, 


116 


THE  WONDERS  OF  SCIENCE. 


and  thank  G-od  that  he  had  come  to  know  so  much 
of  His  goodness  and  glory ; then  he  would  rebuke 
himself,  too,  for  having  remained  so  long  ignorant 
of  the  many  beauties  that  lay  concealed  in  the  wis- 
dom and  exquisite  fitness  with  which  the  phenomena 
of  the  universe  are  linked  together.  “ What  fairy 
tale  of  enchantment,”  he  would  say  to  himself,  “ can 
display  magic  like  this?  What  work  of  human 
invention  can  fill  the  mind  with  such  amazement 
and  delight  at  the  subtlety  of  the  art,  as  the  mind 
feels  when  it  first  learns  the  wondrous  story  of 
Creation  ?” 

When  Humphry  had  read  through  the  books  that 
he  had  obtained  of  Mr.  Tonkin  and  Mr.  Borlase, 
he  proceeded  to  repeat  the  most  striking  of  the  ex- 
periments in  connexion  with  the  subject,  so  as  to 
impress  the  knowledge  more  firmly  on  his  mind. 
But  before  doing  this  he  reviewed  the  whole  mat- 
ter, and  arranged  it  after  his  own  manner — for  he 
was  not  the  boy  to  follow  in  a beaten  track,  and 
found  no  little  delight  in  the  exercise  of  his  own 
genius. 

“ First,”  said  Humphry,  as  he  pondered  over  the 
science  of  heat  in  general,  “ the  sources  of  it  have 
to  be  considered ; that  is  to  say,  whence  is  the  heat 
of  the  earth  derived?  The  universe  is  a vast  re- 
servoir of  caloric,  and  it  is  capable  of  being  evolved, 
by  some  means  or  other,  from  almost  every  substance 


THE  WONDERS  OF  HEAT. 


117 


that  surrounds  us ; and  though  its  production  artifi- 
cially is  now  so  common  that  it  has  lost  all  wonder 
with  us,  there  must  have  been  a time  when  the 
elimination  of  it  from  substances  on  the  earth  must 
have  been  a matter  of  such  amazement  as  to  have 
produced  a feeling  of  awe,  on  the  part  of  the  multi- 
tude, towards  those  who  first  discovered  the  art. 
This,  perhaps,”  the  boy  went  on,  “is  the  origin  of 
the  fable  of  Prometheus,  who  was,  probably,  the 
first  man  who  found  out  the  way  to  kindle  a fire, 
and  so  was  thought  to  have  stolen  the  heat  from 
the  sun.  Tradition  says,  the  first  artificial  fire  was 
produced  by  lightning  striking  a decayed  tree.  Our 
minds  can,  even  now,  almost  conceive  the  terrible 
awe  of  the  people  who  first  witnessed  the  liberation 
of  fire  on  the  earth — who  beheld,  for  the  first  time, 
the  transparent  red  flames  burst  forth  from  the  com- 
bustible and  lick  the  air  like  burning  tongues,  while 
the  smoke  rolled  upwards  from  them  in  dense  leaden 
clouds.  Then  the  intense  pain  felt  on  touching  the 
fire  must  have  made  the  populace  almost  believe 
that  they  had  been  stung  by  demon  serpents,  while 
the  roar  of  the  wind,  as  it  rushed  towards  the  blazing 
mass  to  supply  the  place  of  the  lighter  air  that  had 
been  driven  upwards  by  it,  must  have  sounded  to 
the  people  like  spectral  voices,  and  the  ultimate  dis- 
sipation of  the  huge  solid  substance  into  invisible 
gases  must  have  appeared  like  the  most  marvellous 
magic  to  them.  Thus  it  came  that  men  at  last  got 


118 


THE  WONDERS  OF  SCIENCE. 


to  worship  the  fire,  for  its  wonders  and  its  terror, 
though  we  kindle  it  nowadays  almost  without  a 
thought  or  a fear. 

“ The  sources  of  heat  at  present  known  to  man,” 
continued  the  boy,  as  he  wrote  down  the  divisions 
of  the  subject  in  his  note-book,  “ are  many.  First, 
there  is  the  heat  of  the  sun , and,  perhaps,  that  of 
the  moon ; philosophers,  however,  have  concentrated 
the  moonbeams  upwards  of  300  times,  by  means  of 
a burning-glass,  nearly  3 feet  in  diameter,  and  yet 
the  most  delicate  thermometers  have  shown  not 
the  least  increase  of  temperature.  This  is  said  to 
arise  from  the  feebleness  of  the  light  of  the  moon, 
as  compared  with  that  of  the  sun;  for  the  lunar 
rays  have  been  calculated  to  possess  300,000  times 
less  illuminating  power  than  the  solar  ones,  whilst 
the  light  of  the  sun  itself  has  been  shown  by  ex- 
periment to  have  12,000  times  the  intensity  of  the 
flame  of  a wax-candle,  so  that  a little  fragment  of 
the  great  luminary  the  size  of  such  a flame  would 
possess  the  illuminating  power  of  12,000  wax-can- 
dles ; and,  since  the  diameter  of  the  sun  is  nearly 
four  times  greater  than  the  distance  of  the  earth 
from  the  moon,  this  may  give  us  some  notion  of  the 
vast  flood  of  light  and  (if  the  two  are  connected)  of 
heat  that  are  being  continually  streamed  forth  from 
the  sun  into  the  universe.  Of  the  intensity  of  the 
solar  heat,  the  law  of  the  decrease  of  all  radiant 
matter  enables  us  to  form  some  conception  ; for  this 


THE  WONDERS  OF  HEAT. 


119 


teaches  us  that  the  heat  of  the  sun’s  rays,  after  trav- 
elling to  the  distance  of  the  earth,  must  be  diffused 
over  at  least  300,000  times  a greater  space  than  it 
is  at  the  sun  itself,  and  consequently  that  the  in- 
tensity of  the  heat  must  be  that  number  of  times 
more  highly  concentrated  at  the  sun’s  surface  than 
it  is  on  reaching  our  atmosphere.  Now,  one  of  the 
largest  burning  mirrors  that  have  ever  been  con- 
structed, and  which  had  the  power  of  concentra- 
ting the  sun’s  rays  rather  more  than  17,000  times, 
melted  a piece  of  Pompey’s  pillar  in  less  than  a 
minute,  a piece  of  cast-iron  in  a quarter  of  a min- 
ute, a copper  halfpenny  in  sixteen  seconds,  and  frag- 
ments of  slate  and  tile  in  three  and  four  seconds. 
A lens  that  increased  the  intensity  of  the  sun’s  heat 
about  10,000  times  fused  pieces  of  platinum,  gold, 
asbestos,  quartz,  &c.,  in  three  seconds;  so  that — 
as  the  solar  fire  must,  at  the  sun  itself,  be  30  times 
more  intense  than  the  calorific  power  of  its  rays, 
even  when  thus  concentrated,  at  the  surface  of  the 
earth — it  is  evident  that  the  fury  of  the  sun’s  heat 
must  at  its  source  be  sufficient  to  dissipate  the  most 
obstinate  metals  in  vapour,  and  to  make  the  most 
infusible  of  the  earths  as  liquid  as  glass. 

“Then,  again,  there  is  the  heat  of  the  stars;  for 
if  each  of  these  be  suns,  and  they,  like  our  own 
sun,  give  off  heat,  together  with  light,  while  the 
heat  radiated  by  them  decreases  in  the  same  pro- 
portion as  their  light,  it  is  clear  that  the  united 


120 


THE  WONDERS  OF  SCIENCE, 


beams  of  the  starry  host  must  give  a certain  general 
temperature  to  the  realms  of  space.  This  temper- 
ature philosophers  have  calculated  to  be  as  low  as 
that  at  which  quicksilver  freezes,  and  which  degree 
of  cold  appears  to  be  attained  in  the  Arctic  regions, 
during  the  long  absence  of  the  sun  through  a polar 
winter.  According  to  the  principles  which  regulate 
the  radiation  of  light  and  heat,  it  is  demonstrable 
that  the  starbeams  can  only  maintain  a temperature 
in  infinite  space  which,  when  compared  with  the 
heat  we  derive  from  the  sun,  must  be  as  much  in- 
ferior to  it  as  the  light  of  a moonless  midnight  is  to 
the  light  of  midday  at  the  equator ; and  it  is  plain, 
that  the  rate  at  which  the  earth  cools  clown  or  radi- 
ates back  into  space  the  heat  it  receives  from  the 
sun  must  have  its  limit  in  the  temperature  of  plan- 
etary space  itself,  so  that,  had  this  been  higher  or 
lower,  the  earth’s  surface  must  have  been  hotter  or 
colder  than  it  is. 

“But,  besides  the  preceding  celestial  sources  of 
heat  in  nature,  we  must  also  (if  we  suppose  that 
such  things  as  give  light  to  the  earth  radiate  heat 
as  well  to  it — though  in  ever  so  minute  a degree) 
enumerate  that  peculiar  cone  or  pyramid  of  lumin- 
ous mist  which  is  seen  an  hour  or  two  after  sun- 
set, at  certain  months  of  the  year,  in  the  line  of  the 
ecliptic,  and  to  which  astronomers  have  given  the 
name  of  ‘ the  zodiacal  light?  Travellers  in  tropical 
regions  tell  us  that  this  is  sometimes  so  brilliant 


THE  WONDERS  OF  HEAT.  121 

that  it  seems  a second  sunset,  lasting  almost  to  mid- 
night, and  that  the  clouds  which  are  scattered  over 
the  deep  azure  of  the  distant  horizon  appear  to  flit 
past  the  glowing  nebulosity  as  before  a golden  cur- 
tain, while  above  these  other  clouds  are  seen  reflect- 
ing from  time  to  time  brightly  variegated  colours. 

“Then,  again,  there  are  the  brilliant  corusca- 
tions of  the  aurora  borealis  (or  6 northern  dawn]  or 
‘ polar  light]  as  it  is  sometimes  called),  though  this 
appears  to  be  rather  an  emanation  from  the  earth 
itself  than  any  celestial  phenomenon.  According 
to  the  best  accounts,  the  light  of  the  aurora  exists 
almost  within  the  bounds  of  our  own  atmosphere, 
and  seems  to  stream  from  one  of  the  poles  of  our 
globe,  as  if  the  earth  had  suddenly  acquired  the 
power  of  becoming  self-luminous  like  the  stars  and 
sun.*  This  brilliant  exhalation  is  rendered  more 
interesting  by  the  fact,  that  the  great  Herschel 
himself,  from  repeated  observations  of  the  spots  on 
the  sun,  came  to  the  conclusion  that  such  spots  are 
parts  of  the  dark  solid  body  of  the  sun  itself,  laid 
bare  to  our  view  by  fluctuations  in  the  solar  atmos- 
phere, and  that  from  that  atmosphere  alone  the  light 
and  heat  proceed — the  shining  matter  of  the  sun 

* Professor  Challis,  of  the  Cambridge  University,  calculated 
the  height  of  the  bow  of  light  proceeding  from  the  aurora  (seen 
at  Cambridge,  March  9,  1847)  to  be  177  miles  above  the  surface 
of  the  earth.  The  limits  of  our  own  atmosphere  are  placed,  by 
Sir  John  Herschel,  at  the  100th  part  of  the  diameter  of  the  globe, 
or,  in  round  numbers,  80  miles  above  the  surface. 


122 


THE  WONDERS  OF  SCIENCE. 


being,  not  a fluid,  but  a mass  of  brilliant  or  phos- 
phoric clouds,  glowing  with  the  beams  of  the  lu- 
minous strata  of  the  solar  atmosphere  far  above 
them — in  the  same  manner  as  the  aurora  with  us 
is  said  sometimes  to  illuminate  a stratum  of  clouds 
below  it. 

u It  is  impossible  to  say  what  increase  of  heat  our 
atmosphere  may  derive  from  the  beams  of  the  auro- 
ra and  the  zodiacal  light,  but  as  we  have  no  rea- 
son for  supposing  the  rays  in  these  cases  to  be  des- 
titute of  all  heat,  it  is  evident  that,  when  enumer- 
ating the  several  sources  of  caloric  in  the  universe, 
some  mention  should  be  made  of  them  ; for  who  can 
tell  what  would  have  been  the  effect  upon  the  gen- 
eral stock  of  heat  in  nature  without  such  phenom- 
ena, or  how  low  the  temperature  of  the  earth’s  sur- 
face might  have  been  if  the  heat  of  the  planetary 
space  in  which  it  moves  had  been  less  than  it  is? 

“ But  a far  more  important  source  of  caloric  to 
the  earth  lies  in  its  subterranean  heat , or  the  increase 
of  temperature  which  is  found  to  ensue  as  we  de- 
scend below  the  surface  of  our  globe.  Carefully  con- 
ducted experiments  have  shown  that,  in  our  own  cli- 
mate, the  temperature  increases  about  1°  for  every 
50  feet  that  we  go  down.  At  354  feet  below  the 
ground  the  heat  is  found  to  be  60°,  in  those  parts 
where  the  surface  of  the  earth  itself  has  a mean 
temperature  of  but  50°.  At  792  feet  under  the 
soil  the  thermometer  rises  to  70°;  at  1434  feet  it 


THE  WONDERS  OF  HEAT. 


123 


marks  80°;  at  1872  feet  it  reaches  90°;  whereas 
at  2556  feet  it  is  as  high  as  100°.  Now,  if  this 
rate  of  increase  (viz.  1°  in  every  50  odd  feet) 
continued  uniformly  as  we  descended,  it  would  fol- 
low that,  at  a depth  of  rather  less  than  2 miles, 
water  would  be  constantly  at  the  boiling  point, 
and  at  9 miles  below  the  surface  everything  would 
be  red-hot,  whilst  at  rather  more  than  20  miles  the 
granite  rocks  themselves  would  be  in  a continual 
state  of  fusion.  In  the  ‘ United  Mines’  of  Cornwall 
one  of  the  levels  is  so  hot,  that  though  a stream  of 
cold  water  is  allowed  to  flow  through  it,  in  order  to 
reduce  the  temperature,  the  miners  are  compelled 
to  work  nearly  naked,  and  will  bathe  in  water  at 
80°  to  cool  themselves.  At  the  Tresavean  Mine, 
in  the  same  county,  which  is  nearly  2000  feet  deep, 
the  temperature  is  greater  than  the  intensest  heat 
of  summer  in  the  dog-days. 

u There  is,  however,  no  evidence  to  prove  that 
the  increase  of  temperature  beneath  the  surface 
proceeds  at  a uniform  rate  when  we  descend  to  a 
greater  depth  than  1500  feet  below  the  level  of  the 
sea.  It  will  be  seen  by  the  rates  of  increase  above 
given  that  the  temperature  underground  rises  at 
first  1°  in  every  35  Jr  feet,  whereas  at  great  depths 
the  increase  amounts  only  to  1°  in  every  68  feet ; 
and,  as  far  as  our  observations  have  extended,  the 
subterranean  heat  appears  to  bear  a close  relation 
to  the  thermic  condition  of  the  climate  at  the  sur- 


124 


THE  WONDERS  OF  SCIENCE. 


face;  for  it  is  found,  on  descending  to  a depth  of 
about  60  feet  in  our  own  climate,  the  heat  of  the 
earth  no  longer  fluctuates  with  the  different  seasons, 
but  remains  always  at  the  same  point  during  win- 
ter and  summer,  whilst  at  the  tropics  the  stratum 
of  invariable  temperature  is  situate  at  only  1 foot 
below  the  soil. 

“But  whether  the  subterranean  heat  be  due  to 
the  absorption  of  the  solar  rays,  or  whether  it  arises 
(as  some  have  supposed)  from  a vast  body  of  central 
fire  in  the  earth,  it  is  certain  that  we  have  many 
indications  of  prodigious  elevations  of  temperature 
beneath  the  soil.  These  appear  to  be  due  to  great 
chemical  changes  taking  place  in  the  substances 
forming  the  crust  of  the  earth.  Every  schoolboy 
knows  that  a mixture  of  sulphur  and  iron-filings 
buried  under  the  ground  will,  in  a short  time, 
become  so  heated  as  to  burst  into  flames.  Now 
these  two  materials  form  the  mineral  called  ‘iron 
pyrites,’  which  prevails  through  every  coal-field, 
and  the  moisture  acting  on  these  is  known  to  gener- 
ate heat  enough  to  inflame  neighbouring  combust- 
ibles— many  coal-mines  having  been  set  on  fire 
spontaneously  by  such  means.  In  the  1 United 
Mines,’  where  the  heat  is  found  so  oppressive,  it  is 
undoubtedly  owing  to  the  decomposition  of  immense 
(Quantities  of  pyrites  that  are  known  to  exist  at  a 
short  distance  from  the  works. 

“ Of  the  prodigious  subterranean  heat  existing 


THE  WONDERS  OF  HEAT. 


125 


in  some  parts  of  the  earth  we  have  the  most  un- 
mistakeable  evidence.  In  some  places  boiling  hot 
springs — as  the  Geysers  of  Iceland — issue  from  the 
ground  (in  these  eggs  have  been  cooked  in  4 min- 
utes) ; and  even  in  our  own  country  the  wells  of 
Bath  have  a temperature  of  115°,  while  at  those 
of  Carlsbad,  in  Bohemia,  the  heat  of  the  water  is 
as  high  as  167°.  In  other  parts,  ‘fumaroles ,’  or 
eruptions  of  steam,  burst  from  the  soil;  while  in 
others  there  are  4 solfatarasj  or  jets  of  sulphurous 
vapour;  and  in  others,  again — as  in  the  valleys 
of  the  Eifel,  at  the  lake  of  Laach  in  Germany — 
‘ mofettes,’  or  vast  exhalations  of  carbonic  acid  gas, 
occur.  Further,  there  are  Artesian  fire-springs — 
like  those  termed  £ ho-tsing ’ in  China,  where  a prov- 
ince has  been  lighted  (by  the  gas  issuing  from  them) 
for  several  thousand  years.  Moreover,  eruptions  of 
boiling  acid  mud,  called  ‘ salses ,’  are  not  unfrequent. 
The  volcano  at  Carguaraizo,  in  Peru,  threw  up  a 
torrent  of  hot  mud  in  the  year  1698,  that  covered 
nearly  80,000  acres  of  ground  ; and  in  1797,  an  en- 
tire village  near  Rio  Bambo  was  buried  under  a sim- 
ilar mass. 

“ All  these  phenomena  are  evidences  of  intense 
subterranean  heat,  many  of  them  being  simply  the 
products  of  underground  combustion  : but  lofty  jets 
of  flame  have  likewise  been  known  to  blaze  up  from 
the  earth,  to  such  a height  that  they  could  be  seen 
at  a distance  of  24  miles  from  the  eruption  ; as,  for 


126 


THE  WONDERS  OF  SCIENCE. 


instance,  at  the  village  of  Baldichli,  near  Baku,  on 
the  Caspian  Sea.  During  earthquakes , too,  the 
earth  has  been  known  to  open  and  to  vomit  forth 
flames,  and  gases,  and  enormous  fragments  of  rocks, 
accompanied  with  a noise  of  subterranean  thunder ; 
while  in  some  places  the  heaving  soil  has  been  in- 
flated by  the  force  of  the  compressed  vapours  beneath, 
and  expanded  like  a bladder  filled  with  air.  Such 
was  the  case  among  the  plains  of  Malpais  in  Mexico, 
in  the  month  of  September,  1759,  when  a tract  of 
ground,  3 to  4 miles  in  extent,  rose  up  like  a huge 
bubble — flames  bursting  from  the  earth  the  while 
over  more  than  half  a square  league — and  the  vol- 
cano of  Jorullo  being  formed  at  the  summit. 

“In  volcanoes , or  burning  mountains,  again,  we 
have  manifestations  of  the  intense  elevation  of  tem- 
perature existing  at  certain  places  within  the  crust 
of  the  earth.  The  explosions  from  the  volcano  of 
Guacamayo,  in  South  America,  are  heard  almost 
daily  at  a distance  of  80  miles;  whilst  the  noise  of 
the  detonations  from  one  in  the  Sunda  Islands,  near 
Java,  have  been  distinguished  970  miles  from  the 
spot.  But  the  most  remarkable  instance  on  record 
of  the  fury  and  power  of  the  subterranean  fires  is 
to  be  found  in  the  eruption  of  one  of  the  Icelandic 
volcanoes,  called  ‘ Skaptaa  Jokul,’  which  occurred 
on  the  8th  of  June,  1783.  During  this  eruption 
the  large  river  Skaptaa  entirely  disappeared,  and  the 
day  after,  a torrent  of  burning  lava  rushed  down  the 


V 


THE  WONDERS  OF  HEAT. 


127 


sides  of  the  mountain  and  not  only  filled,  but  over- 
flowed the  channel  of  the  stream,  though  in  many 
places  it  was  600  feet  deep  and  200  feet  broad. 
Then  pursuing  the  course  of  the  river,  the  fiery 
current  poured  over  a lofty  cataract,  and  filled  up 
in  a few  days  an  enormous  cavity  that  the  waters 
had  been  hollowing  out  for  ages.  A short  while 
after  this  another  large  river,  the  Hverfisfliot,  dis- 
appeared from  its  bed,  and  this  was  filled  up  by 
another  fiery  torrent,  which  overflowed  the  country 
in  one  night  to  the  extent  of  more  than  4 miles. 
It  has  been  estimated  that  these  two  streams  of 
burning  molten  rocks  were  together  90  miles  in 
length  by  20  odd  miles  in  breadth,  and,  in  some 
places,  between  500  and  600  feet  deep,  while  there 
were  in  the  aggregate  forty  thousand  million  tons 
of  red-hot  rock  poured  out  of  the  bowels  of  the 
earth  in  the  short  space  of  ten  weeks,  during  which 
the  eruption  lasted.^ 

“ Another  of  the  natural  sources  of  heat  to  the 
earth  is  to  be  found  in  the  electric  discharges  known 
under  the  names  of  forked  and  sheet  lightning. 

/ * 

* To  give  a just  idea  of  this  fearful  event  it  should  be  added, 
that,  at  the  most  moderate  calculation,  1300  human  beings  lost 
their  lives  through  the  eruption;  it  likewise  caused  the  death  of 
20,000  horses,  7000  horned  cattle,  and  130,000  sheep.  The  fish- 
eries on  the  southern  coast  of  the  island,  moreover,  were  destroy- 
ed by  it;  and  Iceland  has  not  to  this  day,  it  is  said,  recovered 
from  the  disastrous  event  of  the  year  of  the  eruption  of  Skaptaa 
Jokul. 


128 


THE  WONDERS  OF  SCIENCE. 


Of  lightning  there  appear  to  be  three  kinds:  (1)  The 
zigzag,  which  is  linear  and  sharply  denned  at  the 
edges ; (2)  the  sheet,  which  illuminates  whole  clouds, 
that  seem  to  open  and  reveal  the  light  within  them  ; 
and  (3)  the  globular , which  appears  in  the  form  of 
fire-balls.  The  two  first  of  these  kinds  last  but  for 
the  thousandth  part  of  a second,  while  the  globu- 
lar form  moves  much  more  slowly.  Of  the  amount 
of  heat  contained  in  each  of  the  different  species  we 
have  no  precise  knowledge,  though,  from  the  ex- 
periments by  which  we  produce  discharges  of  elec- 
tricity artificially,  on  a small  scale,  we  learn  that 
it  must  be  considerable.  If  a spark  which  is  drawn 
from  a small  Leyden  jar,  and  which  has  force  enough 
to  leap  only  some  few  inches  through  the  air,  has 
power  to  inflame  combustibles,  and  even  to  fuse  the 
metals  in  an  attenuated  form,  what  must  be  the 
heat  evolved  from  an  electric  discharge  where  the 
insulating  body  consists  of  whole  acres  of  clouds 
rather  than  a few  square  inches  of  tin-foil,  and 
whence  the  fluid  has  power  to  leap  through  hun- 
dreds of  feet  of  the  atmosphere  towards  the  nearest 
conductor?  That  the  electric  flash  possesses  great 
heating  power,  we  have  repeated  proofs;  for  it 
melts  all  wires  that  are  not  sufficiently  substantial 
to  allow  it  a free  passage,  inflames  decayed  trees, 
overthrows  buildings,  and  often  fuses  even  the 
rocks  themselves  — the  tubes  called  ‘ fulgurites ,’ 
which  occur  in  beds  of  sandstone,  and  consist  of 


THE  WON  DEES  OI  HEAT. 


129 


fused  sand  (glass),  are  known  to  geologists  to  have 
been  produced  by  such  means — -while  at  Funzie,  in 
Fetlar,  the  lightning  is  recorded  to  have  torn  up  a 
rock  105  feetr  long  from  its  bed,  and  hurled  the 
fragments  to  a considerable  distance  from  the  spot. 
Moreover,  the  electric  heat  is  the  greatest  that  we 
are  enabled  to  produce  artificially,  and  so  much  ex- 
ceeds that  of  the  strongest  furnace,  that  platinum, 
which  remains  stubborn  and  infusible  in  a forge  at 
a white  heat,  melts  in  the  arc  of  flame  produced  by 
a powerful  voltaic  battery- — like  wax. 

“ These  are  the  natural  sources  of  heat,”  the 
youth  wrote  on ; “ the  artificial  methods  of  gener- 
ating heat,  however,  are  much  more  various.  We 
can  evolve  heat  by  mechanical  means — as,  for  in- 
stance, by  percussion  or  pressure.  The  blacksmith 
hammers  a nail  until  it  becomes  red-hot,  and  from 
it  he  lights  his  match;  and  in  coining,  the  blank 
piece  of  metal  becomes  greatly  heated  by  the  sud- 
den and  violent  action  of  the  press.  By  the  com- 
pression of  air  in  a small  tube,  by  means  of  a con- 
densing syringe,  a sufficient  quantity  of  heat  may 
be  evolved  to  light  German  tinder ; and  it  has  been 
well  said,  ‘that,  locked  in  a pint  measure  of  air, 
there  exists  sufficient  heat  to  make  several  square 
inches  of  metal  red-hot.’  A piece  of  Xndian-rubber, 
suddenly  and  forcibly  drawn  out,  becomes  warm 
in  consequence  of  the  extension,  as  may  be  easily 
perceived  by  applying  it  to  the  lip  the  moment 

I 


130 


THE  WONDERS  OF  SCIENCE. 


it  is  stretched.  Again,  by  the  concussion  of  a 
Hint  and  steel  so  much  heat  is  produced  that  the 
sparks  which  fly  off  consist  of  small  particles  of 
iron  that  have  been  fused  by  it.  Moreover,  when 
a few  grains  of  fulminating  silver  are  struck  by  a 
hammer,  the  heat  produced  is  sufficient  to  ignite 
gunpowder  and  to  cause  a violent  explosion. 
Again,  friction  is  a prolific  source  of  heat.  The 
Indian  ignites  two  pieces  of  wood  by  rubbing  them 
together ; and  even  two  pieces  of  ice  may  be  made 
tp  melt  each  other  by  the  same  means.  It  has  been 
truly  observed,  too,  that  an  unlimited  supply  of 
heat  seems  capable  of  being  derived  by  friction 
from  certain  materials.  Water  has  been  made  to 
boil  in  two  hours  and  a half,  merely  by  boring 
into  a mass  of  metal  that  was  surrounded  by  the 
fluid. 

u But  not  only  can  we  produce  heat  artificially 
by  mechanical  means  ; we  can  do  so  far  more  plenti- 
fully and  easily  by  chemical  action,  for  it  has  been 
found,  that  whenever  two  or  more  substances  rapid- 
ly combine,  heat  is  invariably  produced.  In  fo- 
mentation (which  is  nothing  more  than  a decom- 
position of  elements  loosely  united,  and  their  re- 
union in  a more  perfect  state  of  combination)  con- 
siderable increase  of  temperature  takes  place.  Dur- 
ing the  making  of  vinegar  there  is  much  heat 
evolved — ’the  temperature  rising,  in  some  processes, 
from  60°  to  85°.  Again,  in  the  process  of  respira- 


THE  WONDERS  OF  HEAT. 


131 


tion  (which  is  merely  the  combination  of  the  char- 
coal in  the  blood,  with  a certain  portion  of  the  air 
drawn  into  the  lungs)  the  heat  evolved  is  sup- 
posed to  be  the  cause  of  our  bodies  remaining  al- 
most at  a constant  temperature.  A little  powder 
of  the  metal  called  antimony  thrown  into  a jar 
of  chlorine  gas  spontaneously  ignites  and  burns 
with  brilliancy,  combining  with  the  gas  so  readily 
that  it  takes  fire  and  produces  at  first  a liquid, 
and  afterwards  a soft  solid  called  the  ‘ butter 
of  antimony.’  Further,  there  is  an  oil-like  fluid 
consisting  of  two  gases  (nitrogen  and  chlorine) 
that  have  been  made  to  unite  with  each  other,  and 
this  compound  has  such  an  affinity  for  combustible 
bodies,  that  even  if  a long  rod,  the  extremity 
of  which  has  been  dipped  in  oil,  be  made  to  touch 
only  a globule  of  it — the  size  of  a mustard-seed — 
confined  under  water,  it  instantly  explodes  with 
a flash  of  light,  and  with  such  violence  that  it 
disperses  the  water  in  a shower,  and  breaks  into 
atoms  the  vessel  in  which  it  is  contained ; so  that 
experienced  chemists  always  protect  the  face  by  a 
mask  when  making  the  experiment.  Again,  if  oil 
of  vitriol  and  spirits  of  wine,  or  if  aqua  fortis  and 
spirits  of  turpentine,  be  suddenly  mixed,  sufficient 
heat  is  set  free  to  ignite  the  spirits.  When  caus- 
tic potash,  too,  dissolves  in  water,  a considerable 
increase  of  temperature  ensues.  So  if  spirits  of 
wine  and  water  are  mixed  together,  the  mixture 


132 


THE  WONDERS  OF  SCIENCE. 


becomes  much  hotter  and  occupies  a smaller  space ; 
whilst  if  four  parts  of  strong  oil  of  vitriol  be  mixed 
with  one  part  of  snow  or  pounded  ice,  the  heat  de- 
veloped is  sufficient  to  boil  water,  whereas  if  one 
part  of  the  acid  be  added  to  four  parts  of  snow,  in- 
tense cold  is  produced.  More  than  this,  if  a piece 
of  clean  platinum  be  immersed  in  a vessel  contain- 
ing a mixture  of  oxygen  and  hydrogen  gases,  such 
intense  heat  is  evolved  that  the  metal  becomes  sud- 
denly red-hot,  and  the  gases  are  made  to  combine 
so  rapidly  that  a violent  explosion  ensues,  and  the 
two  gases  become  water. 

“ But  the  most  ordinary  mode  of  obtaining  heat 
artificially  is  combustion , though  this  is  merely  a 
process  of  rapid  combination  after  all.  It  is  by  the 
heat  evolved  during  the  process  of  combustion  that 
our  houses  are  warmed  in  winter,  our  food  cooked, 
the  steam-engines  of  our  factories  and  mines  set  in 
motion,  our  metals  smelted,  cast,  and  wrought,  our 
glass  made,  our  dishes  hardened,  and  an  infinity  of 
useful  services  rendered  to  us;  indeed,  so  much  do 
we  owe  to  combustion,  that  we  are  unable  to  com- 
prehend the  state  which  man  must  have  been  in 
before  the  method  of  producing  heat  artificially  by 
such  means  was  discovered. 

“Lastly,  there  is  the  heat  generated  by  nervous 
energy;  for  if  the  sole  source  of  warmth  to  the 
animal  frame  lay  in  the  chemical  processes  that 
are  continually  going  on  within  it,  why  should  a 


THE  WONDERS  OF  HEAT. 


133 


suddenly  excited  emotion  (as  in  states  of  anger  and 
blushing)  have  power  to  produce  so  considerable 
an  increase  of  temperature  in  the  human  frame  % 
Indeed  we  have  personal  knowledge,  that  almost  ev- 
ery muscular  movement  produces  sensible  warmth, 
even  as  any  violent  excitement  of  the  mind  is  at- 
tended with  the  same  result.  We  know,  too,  that 
the  injury  of  one  little  thread-like  nerve  can  reduce 
a member  of  the  body  to  a state  of  stony  coldness ; 
and  that  after  death,  when  the  chemical  decomposi- 
tions are  proceeding  as  actively  as  during  life,  the 
body  possesses  no  animal  heat  whatever.”  Physiol- 
ogists, moreover,  have  shown  that,  if  the  respiration 
be  kept  up  artificially  in  an  animal  after  its  head  has 
been  cut  off,  the  blood  becomes  arterialized,  and  the 
several  chemical  changes  go  on  as  during  life — but 
without  the  body  being  in  the  least  warmed  by  them. 


CHAPTER  VII. 


THE  WONDERFUL  DIFFUSION  OF  HEAT. 

When  Humphry  had  written  thus  far  concerning 
the  sources  of  heat  (for  the  boy  was  delighted  to 
note  down  his  thoughts  on  the  various  subjects  he 
was  studying),*  he  began  to  ponder  over  the  sev- 
eral modes  in  which  heat  was  communicated  to 
bodies  removed  from  the  different  sources  of  it ; 
for,  said  he  to  himself,  “ if  there  had  been  no  means 
of  propagating  heat  from  one  part  of  space  to  an- 
other, the  fires  could  not  have  warmed  us,  and  the 
sun  would  have  been  only  a moon  to  our  globe, 
while  we  should  have  been  deprived  of  some  of  our 
most  agreeable  sensations.  Hence,  in  the  consider- 
ation of  such  a subject,  it  becomes  necessary  to  at- 

* The  note-books  of  Davy  during  the  time  of  his  apprenticeship 
have  been  preserved,  and  show  (says  his  brother)  “ the  ardour 
with  which  he  entered  upon  his  studies,  and  the  extensive  reach 
of  his  mind  in  the  various  branches  of  knowledge  which  he  pro- 
posed to  pursue.  One  of  them,  bearing  the  date  of  1795,  is,” 
(Dr.  John  Davy  adds,)  “on  many  accounts,  a literary  curiosity. 
It  is  a small  quarto,  with  parchment  covers.  Outside  one  of  the 
covers  is  the  figure  of  an  ancient  lyre  drawn  with  his  pen,  and  on 
the  other  an  olive  leaf  encircling  a lamp  ; as  if,”  remarks  his 
biographer,  11  in  anticipation  of  his  great  discovery  of  confining 


THE  WONDERFUL  DIFFUSION  OF  HEAT. 


135 


tend  to,  and  distinguish  between,  the  several  ways  in 
which  a body  at  an  elevated  temperature  commu- 
nicates its  heat  to  others  that  are  either  in  contact 
with  it  or  at  a distance  from  it,  as  well  as  the  several 
conditions  which  determine  the  reception  or  absorp- 
tion of  the  heat  by  different  substances. 

flame  in  the  safety-lamp.  At  the  commencement  ot  it  is  the  fol- 
lowing plan  of  study  : 

1.  Theology  ; 

Or  Religion,  Ethics, 
or  moral  virtues, 

2.  Geography. 

3.  My  Profession. 

1.  Botany. 

2.  Pharmacy. 

3.  Nosology. 

4.  Anatomy. 

5.  feurgery. 

6.  Chemistry. 

4.  Logic. 


hi 


Taught  by  Nature. 

“ by  Revelation. 


5.  Language. 

1.  English. 

2.  French. 

3.  Latin. 

4.  Greek. 

5.  Italian. 

6.  Spanish. 

7.  Hebrew. 


6.  Physics. 

1.  The  doctrines  and  properties  of  natural  bodies. 

2.  Of  the  operations  of  nature. 

3.  Of  the  doctrines  of  fluids. 

4.  Of  the  properties  of  organised  matter. 

5.  Of  the  organisation  of  matter. 

6.  Simple  astronomy. 

7.  Mechanics.  9.  History  and  Chronology. 

8.  Rhetoric  and  Oratory.  10.  Mathematics. 

To  give  some  distinct  idea  of  the  bent  of  his  studies  at  this  time,” 
continues  his  brother,  “ I shall  briefly  notice  the  principal  topics 
which  appear  in  this  MS.  volume.  It  opens  with  ‘ Hints  towards 
the  Investigation  of  Truth  in  Religious  and  Political  Opinions, 
composed  as  they  occurred,  to  be  placed  in  a more  regular  manner 
hereafter.’  His  first  essay  is  ‘ On  the  Immortality  and  Immale- 


THE  WONDERS  OF  SCIENCE. 


136 

u Now,  heat  may  be  communicated  from  one  body 
to  another  in  three  different  ways — ■ 

1-  By  emission  of  rays  of  heat  from  a distance ; 

2.  By  conduction  along  the  particles  of  a solid 

body ; 

3.  By  convection  or  circulation  among  the  particles 

of  a fluid. 

riality  of  the  Soul the  second  bears  the  title  of  ‘ Body,  organ- 
ised matter ;'  and  his  third  is  ‘ On  Governments .’  Then  there 
follow  a variety  of  essays  on  metaphysical  and  moral  subjects. 
These  topics  occupy  more  than  one  half  of  the  book  ; the  other 
part,  which  appears  to  have  been  written  after,  commences  at 
the  opposite  end,  inverted.  This  is  devoted  partly  to  religious 
essays  ; but  besides  these,”  adds  Dr.  Davy,  “ there  are  some 
verses  and  the  beginning  of  a romance,  called  ‘ An  Idyl,'  which 
is  in  the  form  of  dialogue,  the  characters  being  ‘ Trevelis  a 
warrior  and  friend  of  Prince  Arthur,  and  Morrobin  a Druid;’ 
the  scene,  ‘ A cliff  at  the  Land’s  End  in  Cornwall.’ 

“From  the  same  source  of  information  — his  note-books — 
it  appears,  that  in  the  beginning  of  the  year  1796  he  entered 
on  the  study  of  mathematics.  One  book  is  almost  entirely 
confined  to  this  subject,  and  he  seems  to  have  finished  the 
elementary  course  in  more  than  twelve  months,  when  he  was 
commencing  the  eleventh  book  of  Euclid,  having  gone  through 
most  of  the  other  branches.  He  engaged  in  these  studies  with- 
out a master,  and  perfectly  voluntary  on  his  part,  from  the  con- 
viction of  their  usefulness  preliminary  to  the  study  of  chemical 
and  physical  sciences.  His  passion  for  poetry  at  the  same  time 
appears  to  have  kept  pace  with  the  expansion  of  his  faculties,  and 
not  to  have  been  damped  even  by  the  application  to  mathematics, 
for  his  early  note-books  contain  many  desultory  verses.  His  ear- 
ly chemical  reading  was  confined  to  two  works  of  a very  differ- 
ent description,  1 Lavoisier's  Elements  of  Chemistry,'  and  1 Nich- 
olson's Dictionary  of  Chemistry.'  This  new  study  seems  very 
soon  to  have  excited  in  his  mind  a most  lively  interest.  He 
was  not  satisfied  with  merely  reading  and  accjuiring  the  ideas  of 
others.  He  criticised  the  theoretical  views  of  the  great  French 


THE  WONDERFUL  DIFFUSION  OF  HEAT-  137 


“ The  propagation  of  heat  by  the  emission  of  heat- 
rays  from  a warm  or  burning  body  at  a distance,  is 
the  one  that  first  demands  attention.  This  mode  of 
communication  is  generally  styled  1 radiation  of  heat,’ 
and  it  is  evident  that  the  heat-rays  emanating  from 
one  body  may  be  communicated  to  another,  either  di- 
rectly, by  the  process  of  transmission  through  the  inter- 
vening substances,  or  indirectly,  by  reflexion  from  the 
surfaces  of  those  opposing  them ; for  the  heat-rays, 
like  those  of  light,  always  proceed  in  a straight  line, 
and  are  susceptible,  likewise,  of  being  reflected  or 
driven  off  at  an  equal  angle  from  polished  surfaces.” 

philosopher  ” (Lavoisier,  the  author  of  the  new  Theory  of  Com- 
bustion, which  was  propounded  only  some  few  years  before)  ; 
“he  doubted,  rejected,  and  advanced  speculations  of  las  own. 
Speculation  appears  to  have  led  him  to  experiment,  and  experi- 
ment to  further  speculation,  with  such  rapid  progress  that  in  a 
few  months  he  had  formed  a new  hypothesis  (concerning  the 
principle  of  heat),  and  flattered  himself  that  he  had  triumphed 
over  an  important  part  of  the  doctrine  of  the  French  school. 

“ Humphry  Davy  himself  writes  in  one  of  his  note-books, 
dated  1799,  ‘ About  twenty  months  ago  I began  the  study  of 
Chemistry.  The  system  of  Lavoisier,  almost  the  only  elementary 
book  in  my  possession,  was  the  first  that  I studied.’  ” That  the 
subject  of  heat  was  the  first  chemical  principle  that  engaged  the 
boy’s  attention  we  have  further  evidence  in  the  fact,  that,  a few 
years  afterwards,  his  “ Researches  on  Heat  and  Light ” were  pub- 
lished in  the  form  of  essays,  in  a miscellaneous  volume  edited  by 
Dr.  Beddoes.  In  the  preface  to  this  work  the  editor  says,  re- 
ferring to  the  views  propounded  by  Davy,  ‘ It  is  not  neces- 
sary, in  praise  or  excuse  of  his  system,  to  add  that  at  the  time 
the  theory  was  formed  the  author  was  under  twenty  years  of  age, 
pupil  to  a surgeon-apothecary  in  the  most  remote  town  of  Corn- 
wall, with  little  access  to  philosophical  books,  and  none  at  all  to 
philosophical  men.’  ” 


138 


THE  WONDERS  OF  SCIENCE. 


Having  settled  thus  much  in  his  own  mind,  and 
arranged  the  subject  with  that  logical  precision 
which  was  a marked  feature  in  the  genius  of  the 
youth,  he  proceeded  to  test  experimentally  the  emis- 
sive energies,  or,  in  other  words,  the  radiating  powers 
of  different  substances. 

For  this  purpose  he  provided  himself  with  a 
square  tin  canister:  one  of  the  four  sides  of  this 
he  brought  to  as  high  a polish  as  he  possibly  could ; 
the  second  side  he  coated  with  a mixture  of  lamp- 
black and  gum-water ; over  the  third  side  he 
pasted  a piece  of  paper,  and  the  fourth  he  covered 
with  glass.  Then,  having  provided  himself  with  a 
thermometer  from  the  surgery  below,  he  proceeded 
to  arrange  the  canister  at  some  distance  from  the 
thermometer,  but  on  a level  with  it.  After  this  he 
filled  the  canister  with  boiling-hot  water,  and  then 
proceeded  to  note  how  the  thermometer  was  affected 
when  the  canister  was  turned  round,  and  each  of 
its  sides  successively  brought  before  the  instrument. 
The  boy  soon  ascertained,  to  his  great  joy,  that  the 
heat  was  thrown  off  most  rapidly  from  the  blackened 
side  of  the  canister ; next  to  that,  he  found  the  sur- 
face covered  with  paper  to  radiate  heat  more  rapidly 
than  the  other  two ; then  the  glass  side  was  discov- 
ered to  possess  more  emissive  power  than  the  polish- 
ed surface,  while  the  polished  surface  itself  had  the 
least  radiating  power  of  all. 

Delighted  with  the  result  of  the  experiment,  and 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  139 

pleased  with  the  knowledge  it  gave  him  as  to  the 
emissive  energies  of  different  substances  for  heat, 
the  boy,  to  assure  himself  that  he  was  not  mis- 
taken, held  his  hand  at  a short  distance  from  the 
canister,  and  caused  the  differently-coated  sides  to 
pass  successively  before  it.  As  he  did  so,  he  could 
feel  the  heat  increase  gradually  as  the  polished  side 
passed  from  before  his  hand  and  the  blackened  one 
came  round  in  front  of  it ; so  that,  had  he  not  been 
aware  of  the  fact,  he  would  hardly  have  believed 
thtit  the  water  in  the  canister  was  as  hot  at  that 
part  where  the  bright  tin  had  been  left  as  it  was 
where  the  side  had  been  blackened  over. 

Next  the  lad  tried  another  modification  of  the 
same  experiment.  Having  blackened  one  canister 
entirely  over,  and  brightly  polished  the  outside  of 
another  which  was  of  the  same  size,  he  filled  the 
two  vessels  with  boiling  water,  and  putting  a ther- 
mometer into  each  he  placed  them  upon  a table  at 
opposite  corners  of  an  empty  room,  and  then  found 
that  the  thermometer  in  the  blackened  vessel  fell 
much  quicker  than  that  in  the  polished  tin  one ; so 
he  now  saw  that  the  reason  why  the  black  side  of 
the  canister  in  the  first  experiment  felt  hotter  than 
the  polished  surface  did  to  his  hand  was,  that  the 
water  there  was  parting  with  its  heat  at  a more 
rapid  rate,  so  that  in  the  entirely  blackened  ves- 
sel it  necessarily  cooled  down  sooner  than  in  the 
bright  tin  one. 


140 


THE  WONDERS  OF  SCIENCE. 


Humphry  was  so  delighted  with  the  truths  he 
had  thus  discovered,  that  he  tried  a number  of 
other  experiments  as  to  the  radiating  power  of  dif- 
ferent substances,  and  at  last  came  to  the  con- 
clusion that  lamp-black,  sealing-wax,  wool,  paper, 
glass,  and  black-lead,  were  much  better  radiators 
of  heat  than  the  metals;  their  power  of  giving 
off  heat  being  in  the  order  in  which  they  are 
here  mentioned — a surface  of  lamp-black  cooling 
quicker  than  one  of  sealing-wax,  and  sealing-wax 
again  more  rapidly  than  writing-paper,  and  so  on 
down  to  the  metals,  which  cooled  the  slowest  of 
all. 

Then,  having  dealt  with  different  substances,  the 
youth  set  to  work  to  ascertain  what  effect  an  alter- 
ation in  the  arrangement  of  the  surface  produced 
in  the  radiating  power  of  the  same  substance.  Ac- 
cordingly he  tarnished,  by  means  of  acid,  one  of  the 
sides  of  the  polished  tin  canister  he  had  previously 
employed,  and  found,  on  filling  the  vessel  again  with 
hot  water,  that  the  dulled  surface  parted  with  its 
heat  quicker  than  the  bright  one.  After  this,  he  pro- 
ceeded to  roughen  another  of  the  sides  with  some 
emery  paper,  and  then,  on  re-filling  the  vessel,  he 
discovered  that  the  scratched  surface  cooled  at  a 
greater  rate  than  the  smooth  polished  one. 

“ So,  then,”  said  young  Humphry  to  himself, 
“not  only  have  different  substances  various  radia- 
ting powers  for  heat,  but  also  a difference  in  the 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  141 


arrangement  of  the  surface  of  the  same  substance  is 
attended  with  a like  effect.” 

Still  the  lad  had  to  examine  the  result  produced 
by  bodies  of  different  densities , and  this  he  did  by 
means  of  a vessel  of  cast-iron  and  one  of  wrought- 
iron,  when  he  found  that  the  cast  metal  parted  with 
its  heat  quicker  than  the  hammered  or  wrought  met- 
al ; so  that  it  was  evident  a lighter  material  was  a 
better  radiator  of  caloric  than  a heavier  one  — for 
the  particles  of  the  iron  in  being  wrought  had  been 
brought  closer  together,  and  the  metal  thus  rendered 
of  greater  density. 

This  done,  Humphry  made  an  entry  in  his  note- 
book, “that  not  only  did  rough  or  dull  surfaces  part 
with  their  heat  quicker  than  smooth  or  bright  sur- 
faces, but  that  light  bodies  were  better  radiators  than 
heavy  ones.” 

The  young  experimentalist  was  overjoyed  with  the 
progress  he  had  made,  and  he  would  have  rambled 
off  into  a number  of  speculations  as  to  the  effect 
which  the  principles  he  had  discovered  must  produce 
in  nature  (for  he  saw  that  the  different  surfaces  of 
different  countries  must  yield  a like  result);  but  he 
was  too  intent  on  pursuing  the  investigations  he 
had  undertaken  to  allow  himself,  yet  awhile,  to  ap- 
ply them  to  the  explanation  of  terrestrial  phenom- 
ena. Moreover,  he  had  still  to  learn  the  different 
rates  of  cooling  among  bodies  in  the  air  apd  in  a 
vacuum.  To  do  this,  however,  an  air-pump  was 


142 


THE  WONDERS  OF  SCIENCE. 


necessary,  and  how  he  was  to  obtain  such  an  appa- 
ratus puzzled  his  ingenuity  for  a considerable  time. 

At  length  the  youth  remembered  to  have  seen  a 
large  syringe  among  Mr.  Tonkin’s  instruments,  and 
having  obtained  the  loan  of  this,  he  applied  it  to  a 
stand,  and  used  it  as  the  pump  for  extracting  the 
air  from  the  receiver.  When  the  instrument  was 
complete,  Humphry  found  that  bodies  which  took 
between  two  and  three  minutes  to  cool  in  the  air 
were  as  long  as  five  minutes  in  parting  with  the 
same  quantity  of  heat  in  a vessel  from  which  all  the 
air  had  been  exhausted.  So  he  now  perceived,  that 
the  same  substances  gave  off  their  heat  twice  as 
quick  in  the  open  air  as  they  did  in  vacuo. 

The  next  step  was  to  ascertain  the  different 
amounts  of  radiation  among  different  bodies  on  the 
earth.  For  this  purpose  the  boy  borrowed  as  many 
thermometers  as  he  could  procure  among  his  friends 
in  the  town  ; and  early  one  evening,  after  the  sun 
had  declined,  and  when  the  soil  was  parting  with 
the  heat  it  had  received  in  the  course  of  the  day,  he 
proceeded  to  test,  by  means  of  the  instruments,  the 
several  rates  at  which  the  various  substances  upon 
the  earth  were  being  cooled  down.  One  of  the 
thermometers  he  suspended  in  the  air  four  feet  above 
the  grass -plat  in  the  garden  at  the  back  of  the 
doctor’s  house ; another  he  placed  on  some  wool 
which  he  had  spread  on  a raised  board ; another  lie 
deposited  on  the  surface  of  the  raised  board  itself ; 


THE  WONDERFUL  DIFFUSION  OF  IIEAT.  143 


and  a fourth  he  rested  on  the  grass-plat.  Shortly 
afterwards  he  proceeded  to  note  the  temperatures 
indicated  by  the  several  thermometers  in  the  differ- 
ent  situations,  when  he  found  that  the  one  in  the 
air  stood  at  rather  more  than  60°,  while  that  rest- 
ing on  the  wool  was  at  54^-°,  and  that  lying  on  the 
hoard  at  57°,  whereas  the  one  on  the  grass-plat 
marked  only  51°.  In  an  hour  or  two  after  this,  the 
boy  noticed  that  the  blades  of  grass  were  suffused 
with  dew,  and  that  the  fibres  of  the  wool  also  were 
beaded  over  with  little  drops  of  moisture,  but  to  a 
less  extent  than  the  grass,  while  the  surface  of  the 
board  remained  almost  dry. 

“So  then,”  he  said  to  himself,  uivool  is  a better 
radiator  than  ivood,  and,  cooling  quicker,  condenses 
the  moisture  of  the  air  more  rapidly  upon  it;  hut 
grass  again,  as  the  thermometer  showed,  cooled  quick- 
er even  than  the  wool,  and  therefore  collects  more 
dew  than  either.” 

This  induced  young  Humphry  to  try  another  ex- 
periment, in  order  to  ascertain  whether  those  bodies 
which  cooled  most  rapidly  collected  the  most  dew 
on  their  surfaces.  Accordingly  he  placed  a piece  of 
bright  polished  metal  and  a piece  of  glass  (for  the 
surfaces  of  these  substances  were  nearly  the  same) 
on  the  gravel-path,  and  was  delighted  to  perceive 
that  in  a short  time  the  glass  was  covered  with  moist- 
ure while  the  metal  remained  perfectly  dry.  A strip 
of  flannel  was  then  put  beside  the  other  two,  and, 


144 


THE  WONDEKS  OF  SCIENCE. 


being  a good  radiator,  it  soon  became  spotted  with 
dew-drops.  After  this  the  boy  coated  the  piece  of 
polished  metal  with  lamp-black,  and  found  it  then, 
like  the  others,  capable  of  condensing  the  moisture 
of  the  air  upon  its  surface. 

“It  is  as  I expected,”  cried  the  lad;  “the  dew 
which  the  ancients  imagined  to  be  shed  from  the 
stars  is  simply  the  condensation  of  the  vapour  in  the 
atmosphere  upon  cold  surfaces ; and,  consequently, 
those  bodies  which  have  the  greatest  radiating  pow- 
er, and  so  become  cold  the  quickest,  are  found  to 
have  the  largest  deposition  of  dew  formed  upon 
them,  while  those  which,  like  polished  metals,  part 
with  their  heat  but  slowly,  and  so  remain  for  a long 
time  at  the  same  temperature,  have  but  little  moist- 
ure condensed  upon  their  surface.  The  deposition 
of  dew,”  he  went  on  musing,  “is  precisely  similar 
to  the  condensation  of  moisture  that  occurs  on  the 
outside  of  a bottle  of  very  cold  water  when  brought 
into  a warm  room.  The  cold  surface  of  the  glass 
abstracts  heat  from  the  vapour  in  the  air  of  the 
apartment,  and  so  causes  it  to  be  condensed  in  the 
form  of  little  watery  globules  on  the  surface.  In 
the  same  manner  the  earth,  parting  at  night  with 
the  heat  it  has  received  during  the  day  from  the 
sun,  becomes  cooler  than  the  atmosphere  above  it 
- — for  thermometers  show,  that  when  the  grass  is  at 
51°  in  the  evening,  the  air  only  four  feet  above  it  is 
more  than  60° — and  accordingly  the  cold  surface  of 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  145 

the  blades  acts  upon  the  vapour  in  the  atmosphere, 
precisely  the  same  as  the  outside  of  the  cold  bottle 
does  upon  the  air  in  a warm  room.” 

So  pleased  was  the  lad  with  the  insight  that  his 
investigations  had  given  him  into  some  of  the  mys- 
teries of  nature,  that  he  continued  his  experiments 
on  this  subject  for  many  nights ; and  in  the  course 
of  these  he  found,  that  not  only  had  different  bodies 
different  dew-collecting  powers,  but  that  different 
colours  even  possessed  the  same  property;  for  on 
exposing  a piece  of  yellow,  of  green,  of  red,  and  of 
black  glass  to  the  night  air,  he  perceived  that  the 
moisture  appeared  first  on  the  yellow  glass,  then  on 
the  green , but  that  none  at  all  showed  itself  on 
either  the  red  or  Hack  glasses. 

To  his  astonishment,  however,  he  at  length  dis- 
covered, that  when  the  evenings  were  cloudy , and 
there  seemed  to  be  a greater  quantity  of  moisture  in 
the  atmosphere,  the  pieces  of  flannel  and  glass,  and 
little  piles  of  swan’s-down  with  which  he  had  stud-* 
ded  the  gravel-walk,  remained  unmoistened  with 
dew ; whereas,  when  the  nights  were  clear  and  ap- 
parently dry , they,  one  and  all,  with  the  exception 
of  the  polished  metals,  became  rapidly  suffused  with 
moisture.  This  for  awhile  entirely  baffled  the  boy’s 
comprehension.  “ Plow  came  it  that  more  dew  was 
deposited  on  dry  clear  nights  than  on  dull  damp 
ones'?”  Surely,  such  being  the  case,  the  dew  can- 
not be  said  to  proceed  from  the  vapour  in  the  atmos- 

K 


146 


THE  WONDERS  OP  SCIENCE. 


phere;  for  if  it  does,  reasoned  Humphry,  it  is  evi- 
dent that  when  there  is  more  moisture  in  the  air 
there  should  be  more  dew  deposited  on  the  earth. 

At  length  it  struck  the  boy  that,  perhaps,  the 
clouds  themselves  might  interfere  in  some  way  or 
other  with  the  result ; so  the  next  fine  clear  night 
he  strewed  the  gravel-walk,  as  before,  with  frag- 
ments of  such  substances  as  he  had  already  found  to 
be  the  best  collectors  of  dew ; and  then,  at  the  other 
end  of  the  path,  he  placed  pieces  of  the  same  sub- 
stances under  a small  awning,  which  he  made  out 
of  his  pocket-handkerchief,  fastened  at  each  corner 
to  a short  stick.  This  he  did  in  order  to  see  what 
effect  would  be  produced  by  screening  bodies  from 
the  sky — since  the  clouds,  he  fancied,  might  act  in 
some  such  manner. 

On  returning  to  the  garden  after  a short  interval, 
Humphry  was  rejoiced  to  find  that  there  was  a co- 
pious deposition  of  dew  on  the  pieces  of  glass  and 
wool  that  he  had  left  exposed  to  the  sky,  while  the 
surfaces  of  those  which  were  screened  by  the  little 
awning  above  them  remained  perfectly  dry. 

“Yes,”  cried  the  lad,  “ the  clouds  do  act  as  screens. 
They  give  back,  perhaps,  some  of  the  heat  that  the 
earth  at  night  is  radiating  into  space,  and  so  pre- 
vent bodies  cooling  down  as  rapidly  as  they  other- 
wise would.” 

However,  to  satisfy  himself  that  the  clouds  real- 
ly did  interfere  with  the  radiation  of  bodies  on  the 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  147 

earth,  Humphry  arranged  an  apparatus  for  testing 
the  point.  This  consisted  of  a thermometer,  the 
bulb  of  which  was  first  incased  in  wool  (for  that 
substance  he  knew  to  part  readily  with  heat)  and 
afterwards  fixed  in  the  focus  of  a small  concave 
mirror.  Then  on  the  next  windy  night,  when  the 
clouds  were  drifting  swiftly  across  the  sky — leaving 
the  heavens  occasionally  clear,  and  occasionally  hid- 
ing the  light  of  the  stars — the  anxious  lad  turned 
the  mirror  towards  the  blue  vault  above,  and,  on 
doing  so,  he  could  hardly  repress  his  glee  as  he 
beheld  the  quicksilver  in  the  tube  of  the  thermom- 
eter descend  and  ascend,  each  time  the  sky  became 
clear  or  clouded.  Though,  by  means  of  another 
thermometer,  he  knew  the  temperature  of  the  sur- 
rounding atmosphere  to  be  60°,  Humphry  never- 
theless found  that,  when  the  sky  was  unclouded , the 
mercury  in  the  one  attached  to  the  mirror  indica- 
ted only  45°,  whilst  immediately  that  a cloud  passed 
over  the  firmament , and  so  prevented  the  bulb  from 
parting  with  its  heat,  the  quicksilver  rose  rapidly 
again  to  the  temperature  of  the  air  around.  So  in- 
tensely did  Humphry  exult  in  the  result  of  this  ex- 
periment, that  he  remained  long,  watching  the  ther- 
mometer rise  and  fall,  as  the  clouds  swept  one  after 
another  across  the  sky. 

The  next  day,  Humphry,  now  that  he  had  made 
himself  acquainted  with  the  circumstances  that  reg- 
ulated the  emission  or  radiation  of  heat  from  bodies, 


148 


THE  WONDERS  OF  SCIENCE. 


began  to  turn  his  attention  to  the  reflexion  of  it  from 
such  substances  as  impeded  the  progress  of  the  rays ; 
“ for,”  said  he,  “ if  bodies  at  an  elevated  temperature 
have  the  power  of  sending  out  rays  of  heat  in  all 
directions — in  the  same  manner  as  luminous  bodies 
emit  rays  of  light — -it  follows  that  substances  oppos- 
ing the  passage  of  the  heat-rays  must  either  absorb 
them,  and  so  become  heated  themselves  — or  they 
must  transmit  them  and  so  allow  the  rays  to  proceed 
in  their  original  direction — -or  else  they  must  reflect 
them  and  so  bend  them  into  another  course.” 

For  the  study  of  the  reflexion  of  heat  the  lad  pro- 
cured two  concave  mirrors,  made  of  tin-plate  and 
about  1 foot  in  diameter.  These  he  arranged  so  as 
to  slide  up  and  down  a pillar,  to  which  they  were 
respectively  attached.  Thus  provided,  Humphry 
proceeded  to  place  a small  “Florence  flask,”  filled 
with  hot  water,  in  the  focus  of  one  of  the  mirrors, 
while  in  the  other  focus  he  arranged  a thermome- 
ter after  this  fashion : 


Now,  though  the  mirrors  were  some  feet  apart,  the 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  149 

mercury  in  the  tube,  to  the  boy’s  great  delight,  rose 
almost  to  the  heat  of  the  boiling  water  in  the  flask. 

After  a few  moments’  reflection,  the  lad  fancied 
the  effect  might  perhaps  be  due  to  the  radiation  of 
the  heat  from  the  flask  itself,  rather  than  to  the  re- 
flexion of  it  from  the  mirrors.  So,  to  satisfy  him- 
self whether  or  not  such  were  the  case,  he  placed 
a sheet  of  pasteboard  immediately  in  front  of  the 
mirror  near  the  thermometer,  and  thus  prevented 
any  rays  being  reflected  from  the  one  to  the  other. 
No  sooner,  however,  had  he  done  so  than  the  mer- 
cury was  seen  to  fall  in  the  tube — even  though  the 
source  of  heat  was  as  near  to  the  thermometer  as 
before  ; but  directly  he  removed  the  pasteboard  from 
between  the  mirror  and  the  thermometer,  the  quick- 
silver rose  rapidly  again,  and  stood  at  the  same  num- 
ber of  degrees  as  it  previously  did. 

Having  convinced  himself  upon  this  point,  he 
then  drew  the  thermometer  away  from  the  focus 
and  nearer  to  the  heated  flask,  so  that,  if  the  effect 
were  due  to  radiation,  the  mercury,  as  it  approach- 
ed the  source  of  heat,  should  rise  higher  in  the  tube. 
The  contrary  result,  however,  was  found  to  ensue; 
and  it  will  be  seen  on  reference  to  the  preceding  en- 
graving, that  by  radiation  only  a few  of  the  heat- 
rays  (which  are  indicated  by  the  diverging  unbroken 
lines)  would  fall  upon  the  thermometer,  whereas  by 
reflexion  a much  larger  number  of  such  rays  become 
concentrated  upon  the  bulb  in  the  focus  of  the  op-  \ 


150 


THE  WONDERS  OF  SCIENCE. 


posite  mirror — as  shown  by  the  dotted  lines  in  the 
diagram. 

Humphry  was  now  anxious  to  see  whether,  by 
reflexion  of  the  heat-rays,  he  could  ignite  combust- 
ible bodies  at  a distance ; but  for  this  purpose  he 
changed  the  situation  of  the  mirrors,  arranging 
them  vertically  one  above  the  other,  instead  of  hor- 
izontally, or  each  on  a 
level  with  the  other,  as 
before.  Then  he  made 
a small  basket  of  iron 
wire,  and  having  filled 
this  with  burning  char- 
coal, he  suspended  it 
below  the  upper  mir- 
ror, so  that  it  hung 
exactly  in  its  focus, 
whilst  above  the  lower 
mirror  he  fixed  a small 
piece  of  phosphorus, 
and  this  was  exactly  in 
the  focus  also.  Thus, 
on  the 
comple- 
tion 

the  arrangement,  the  boy  was  as  astonished  as  he 
was  delighted  to  perceive  that  the  phosphorus  was 
immediately  inflamed  by  the  reflected  rays  of  heat. 
Some  fulminating  silver  was  then  exploded  in  like 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  151 


manner.  After  this  Humphry  boiled  some  water 
in  a flask  that  he  substituted  for  the  piece  of  phos- 
phorus in  the  focus  of  the  lower  mirror,  and  finally 
cooked  a chop,  by  the  same  means,  at  some  con- 
siderable distance  from  the  fire. 

Next,  instead  of  the  two  mirrors,  he  rolled  up  a 
sheet  of  bright  gilt  paper,  with  the  metallic  side  in- 
wards, into  the  form  of  a long  cone  or  funnel,  so  that 
the  opening  was  larger  at  one  end  than  at  the  other ; 
then  holding  the  larger  end  towards  a clear  fire,  he 
found  the  rays  of  heat  were  concentrated  into  a focus 
at  a little  distance  beyond  the  smaller  end,  and  there 
he  caused  a bit  of  phosphorus  again  to  inflame,  by 
means  of  the  reflected  heat.  The  subjoined  diagram 
exhibits  the  arrangement.* 


Humphry  now  began  to  wonder  what  effect  would 

* A lucifer  match  may  be  conveniently  employed  for  the  same 
purpose,  and  it  will  be  found  that  the  match,  by  means  of  the  cone, 
may  be  inflamed  at  a greater  distance  from  the  fire  than  it  could 
possibly  be  without  it. 


152 


THE  WONDERS  OF  SCIENCE. 


be  produced  by  a piece  of  ice  placed  in  the  focus  of  one 
of  the  mirrors ; and  he  thought  for  a long  time  wheth- 
er the  rays  of  cold  would  be  reflected  from  the  ice,  as 
those  of  heat  had  been  from  the  hot  water  and  the 
burning  charcoal.  As  the  winter  had  long  set  in,  he 
found  no  difficulty  in  obtaining  such  a piece  as  he  re- 
quired from  one  of  the  neighbouring  ponds,  and  then 
arranging  the  mirrors  as  before,  he  placed  it  in  the  fo- 
cus of  one  of  them,  while  in  that  of  the  other  he  fixed 
the  thermometer  which  he  had  previously  employed. 

To  the  lad’s  astonishment  he  discovered  that  the 
mercury  immediately  began  to  fall,  and  at  length 
stood  at  32°,  or  the  freezing  point.  “ So  then !” 
he  cried,  “it  is  possible  to  reflect  rays  of  cold  as 
well  as  those  of  heat.  And  yet,”  said  he  to  himself, 
after  musing  for  a while,  “ is  it  the  ice,  after  all, 
that  is  radiating  cold  to  the  thermometer,  or  the 
thermometer  itself,  which,  being  warmer  than  the 
frozen  water,  is  really  and  truly  radiating  heat  to  the 
ice  f’  If,  instead  of  the  thermometer,  he  had  placed 
a red-hot  body  in  the  one  focus,  while  the  ice  re- 
mained in  the  other,  Humphry  knew  well  enough 
that  the  warmer  body,  as  it  became  cool,  would  be 
giving  off  heat  to  the  colder  one.  “Why  then,”  he 
asked  himself,  “ should  he  fancy  that  the  thermom- 
eter itself — because  it  was  only  a few  degrees  warmer 
than  the  ice - — lacked  the  power  of  parting  with  its 
heat  to  the  colder  body,  in  the  same  manner  as  the 
red-hot  charcoal  V* 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  153 

The  lad  was  soon  convinced  of  his  previous  fal- 
lacy ; and  when  he  saw  that  the  apparently  contra- 
dictory effect  was  no  anomaly  after  all,  he  could 
hardly  refrain  from  smiling  at  the  simplicity  which 
had  led  him  to  believe  at  first  that  rays  of  cold  were 
reflected  from  the  ice  to  the  thermometer,  instead 
of  the  rays  of  heat  being  given  off  by  the  thermom- 
eter to  the  ice. 

As  yet,  however,  Humphry  had  experimented  con- 
cerning the  reflexion  of  heat  with  mirrors  only  of 
polished  metal ; and  one  day,  when  he  was  recount- 
ing to  Mr.  Tonkin  the  curious  effects  he  had  pro- 
duced, the  old  gentleman  asked  the  lad  what  he  im- 
agined would  have  been  -the  effect  if,  instead  of  metal 
mirrors,  he  had  used  glass  ones. 

Humphry  answered  confidently,  that,  as  the  re- 
sults were  due  only  to  the  reflexion  of  the  rays  from 
-the  concave  surface,  a glass  mirror,  of  course , would 
have  given  precisely  the  same  effects  as  the  metal 
ones. 

“Try  it,”  was  all  the  old  man  said,  as  he  smiled 
at  the  positiveness  of  the  boy’s  reply. 

Nor  was  the  young  experimentalist  long  in  doing 
so,  for  he  saw  by  Mr.  Tonkin’s  manner  that  some 
strange  difference  in  the  effect  would  ensue — though 
for  the  life  of  him  he  could  not  divine  what  it  was 
to  be. 

Accordingly,  at  the  earliest  opportunity,  the  boy 
substituted  the  glass  concave  mirror,  which  Mr. 


154 


THE  WONDERS  OF  SCIENCE. 


Tonkin  had  lent  him  for  the  purpose,  for  one  of 
the  metal  ones  which  he  had  previously  employed ; 
then  filling  the  little  wire  basket  with  red-hot 
charcoal,  as  before,  and  hanging  it  in  the  focus 
of  the  upper  mirror,  he  once  more-  suspended  a 
piece  of  phosphorus  in  the  focus  of  the  lower  mir- 
ror, which  was  now  of  glass  instead  of  metal.  To 
his  utter  amazement,  however,  the  phosphorus  was 
no  longer  capable  of  being  inflamed  in  such  a man- 
ner. 

It  was  but  the  work  of  a moment  to  remove  the 
combustible  from  the  focus  of  the  glass  mirror,  and 
to  place  a thermometer  there  in  its  stead ; and  this 
soon  showed  that  there  was  now  little , if  any , heat 
reflected. 

“ How  wonderful !”  cried  the  startled  boy. 
“What  can  be  the  cause  of  it?  I’ll  arrange  the 
mirrors  differently,”  he  added,  “and  see  if  I can  find 
it  out.” 

But  no  sooner  did  Humphry  put  his  finger  on 
the  glass  than  he  drew  it  suddenly  back,  as  he  ex- 
claimed, “ How  hot  the  lower  mirror  has  become ! 
and  I remember  when  I used  the  metal  one,  that 
I was  surprised  to  find,  on  removing  it,  though 
the  heat  was  sufficient  to  boil  water  and  ignite 
bodies  in  its  focus,  the  metal  surface  of  the  mirror 
itself  was  scarcely  warmed.  But  now  that  glass  is 
used,”  he  went  on,  “ the  mirror  itself  is  rendered 
hot , while  in  the  focus  of  it  there  is  scarcely  any 


Humphry’s  experiments  on  the  diffusion  of  heat. — Page  157. 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  157 

perceptible  increase  of  temperature.  So,  then,”  he 
added,  “the  glass  absorbs  the  heat-rays,  and  there- 
fore does  not  reflect  them,  while  the  metal  on  the 
other  hand  reflects , because  it  does  not  absorb  them. 
Still  it’s  very  strange,”  mused  Humphry,  as  he  pro- 
ceeded to  blacken  a small  card,  “ for  the  glass  mir- 
ror must  reflect  the  light  of  the  fire,  though  it  absorbs 
the  heat  from  it.  I’ll  try  whether  such  is  the  case 
or  not.” 

The  card  was  then  placed  in  the  focus,  and  a 
bright  spot  of  light  was  seen  shining  like  silver  in 
the  centre  of  the  blackened  surface. 

“ Yes,”  cried  the  lad,  “ it  reflects  the  light,  but 
not  the  heat  of  the  fire.  How  strange ! I wonder 
whether  the  same  effect  would  be  produced  by  the 
sun’s  rays !” 

Accordingly  the  next  day,  when  the  sun  was 
shining  brightly,  Humphry  arranged  the  mirror  in 
the  garden,  so  that  the  beams  might  be  concentrated 
in  its  focus ; and  then,  to  his  greater  astonishment, 
he  found  that  he  could  inflame  combustibles  by  the 
solar  heat  with  the  glass  mirror,  in  the  same  manner 
as  he  had  previously  done  by  artificial  heat  with  the 
metal  ones. 

“ The  light  and  heat  of  the  sun,  then,”  said  Hum- 
phry, as  he  stood  watching  the  white  fumes  of  the 
burning  phosphorus  rise  in  the  air,  “are  capable 
of  being  reflected  by  glass,  whereas  the  light  only 
of  an  artificial  fire  can  be  concentrated  into  a fo- 


158 


THE  WONDERS  OF  SCIENCE. 


cus  by  it— -the  heat  in  the  latter  case  being  absorb- 
ed.” 

The  metal  mirror,  likewise,  was  found  to  possess 
the  power  of  reflecting  both  the  solar  light  and  heat, 
in  the  same  manner  as  it  had  been  before  made  to 
reflect  both  the  light  and  heat  of  an  artificial  fire. 

The  experiment  with  the  glass  mirror,  however, 
clearly  showed  that  solar  heat  differed  in  some  way 
or  other  from  terrestrial  heat ; but  how,  was  a source 
of  continual  wonder  to  the  lad. 

From  the  reflexion  of  heat,  Humphry  proceeded  to 
the  transmission  of  it. 

Light  passes  readily  through  certain  substances, 
which  are  therefore  said  to  be  transparent , while 
others  impede  the  progress  of  the  beams,  and  are 
consequently  called  opaque.  “ Is  there,  then,”  mused 
the  boy,  “ such  a property  as  transparence  and  opacity 
for  heat,  as  well  as  light,  among  bodies  ? Are  some 
substances  pellucid,  as  it  were,  to  heat  like  they  are 
to  light?  and  are  some  as  impermeable  to  the  one 
as  they  are  to  the  other  ?” 

The  lad  knew  well  that  the  heat  of  the  sun  was 
capable  of  being  transmitted  through  glass  as  well 
as  its  light,  for  he  had  often  concentrated  the  solar 
beams  by  means  of  a magnifying  or  “ burning”  lens, 
as  it  is  called : glass,  therefore,  was  transparent  to 
the  solar  heat  as  well  as  light ; but  was  it  so  to  the 
rays  of  artificial  heat  ? 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  159 

To  ascertain  this,  Humphry  borrowed  old  Dr. 
Tonkin’s  large  reading  lens,  and  held  it  before  the 
fire  so  that  the  focus  fell  upon  the  bulb  of  a ther- 
mometer. But  though  the  light  of  the  burning  coals 
was  seen  concentrated  into  a bright  spot  upon  the 
bulb,  still  the  mercury  in  the  tube  gave  no  indica- 
tions of  any  increase  of  temperature.  The  lens,  how- 
ever, which  was  scarcely  warmed  when  the  sun’s  rays 
passed  through  it,  became  greatly  heated  when  the 
rays  of  the  artificial  fire  were  made  to  fall  upon  it — 
thus  showing,  that  while  it  transmitted  the  solar  heat 
it  absorbed  the  terrestrial. 

It  was  evident,  therefore,  that  though  the  heat  of 
the  sun  has  the  power  of  passing  freely  through  glass, 
artificial  heat , on  the  other  hand,  is  completely  stop- 
ped by  it. 

Humphry  then  thought  he  should  like  to  try  the 
effect  of  a piece  of  black  glass,  for  this  would  be 
perfectly  opaque  to  light,  and  he  longed  much  to 
see  whether  it  woukl  be  equally  impermeable  to 
heat.  On  holding  a square  piece  before  the  fire,  the 
boy  was  surprised  to  perceive  the  thermometer  he 
had  arranged  behind  it  rise  rapidly,  thus  showing 
that  though  black  glass  was  in-transparent  to  light , it 
was  by  no  means  opaque  to  heat.  That  the  quick- 
silver was  made  to  mount  in  the  tube  solely  by  the 
influence  of  the  heat-rays  which  traversed  the  black 
glass — and  not  by  any  indirect  radiation  from  the 
fire — Humphry  assured  himself,  by  placing  a piece 


160 


THE  WONDERS  OP  SCIENCE. 


of  white  glass,  of  the  same  size  and  thickness  as  the 
black  one,  before  the  thermometer : the  quicksilver, 
however,  was  immediately  seen  to  fall.  “ How  mar- 
vellous is  this !”  he  exclaimed.  “ Light  and  heat, 
then,  are  capable  of  being  separated  one  from  the  oth- 
er ; and  there  are  bodies  in  nature  which,  like  white 
glass,  are  transparent  to  light,  but  opaque  to  heat ; 
while  there  are  others,  like  black  glass,  that  allow 
the  heat-rays  to  pass  through  them,  though  they 
are  incapable  of  being  traversed  by  the  luminous 
ones.” 

The  boy  was  so  full  of  the  new  truth  that  had 
thus  become  impressed  upon  his  mind,  that  he  hur- 
ried off  to  Mr.  Tonkin  to  confer  with  him  on  the 
result.  From  him  Humphry  learnt  that  there  were 
other  substances,  besides  glass,  that  gave  equally  cu- 
rious effects  — the  most  striking  of  these,  the  old 
gentleman  told  the  boy,  were  alum  and  rock-salt , for 
though  both  were  transparent  to  light,  they  had  by 
no  means  the  same  power  of  transmitting  heat ; for 
it  would  be  found  that  while  a small  plate  of  rock- 
salt  allowed  the  rays  of  heat  to  pass  almost  freely 
through  it,  a similar  plate  of  alum  was  nearly  im- 
permeable to  them. 

The  young  philosopher  was  not  long  in  trying 
the  experiment.  Having  procured  two  such  plates 
as  Mr.  Tonkin  had  advised,  he  used  them  as  small 
screens  in  front  of  the  fire,  and  found  that  a ther- 
mometer behind  the  rock-salt  rose  rapidly ; whereas, 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  161 


behind  the  alum,  it  was  scarcely  affected,  for  the 
heat  was  nearly  all  stopped  by  it. 

The  possibility  of  separating  heat  from  light 
made  a powerful  impression  upon  the  ardent  boy, 
and  he  wondered  whether  he  could  arrive  at  the 
same  result  with  the  solar  beams  as  he  had  with 
the  rays  of  an  artificial  fire.  For  a long  time  he 
pondered  over  the  matter,  and  conceived  and  tried 
a number  of  fruitless  experiments  in  connexion 
with  it. 

At  length,  however,  he  remembered  to  have  read 
somewhere,  that  by  means  of  a glass  prism  the 
beam  of  white  light  proceeding  from  the  sun  might 
be  separated  into  all  the  colours  of  the  rainbow. 

Accordingly  he  set  to  work  to  repeat  the  experi- 
ment. Having  darkened  his  room  he  made  a hole 
in  the  window-shutter,  and  placed  behind  it  a glass 
prism,  with  one  of  the  sharp  edges  downwards  and 
one  of  the  flat  sides  uppermost,  as  shown  in  the  an- 
nexed illustration : 


Immediately  that  the  arrangement  was  complete, 

L 


162 


THE  WONDERS  OF  SCIENCE. 


and  the  beam  from  without  fell  on  the  glass  within, 
the  wall  on  the  opposite  side  was  iridescent  with  a 
strip  of  variegated  light,  as  if  a slice  of  a bright 
rainbow  were  clinging  to  it.  The  lower  end  of 
the  luminous  band  was  a rich  warm  red,  and  this 
passed,  by  a tint  of  orange,  into  a bright  yellow, 
which  again  died  away,  by  deepening  hues  of  green, 
into  a narrow  strip  of  dark  blue,  while,  at  the  up- 
per end,  the  indigo  tint  became  warmed  into  a brill- 
iant edging;  of  violet. 

When  the  rapture  of  the  boy  on  first  beholding 
the  sight  had,  in  a measure,  subsided,  he  proceeded, 
by  means  of  a thermometer,  to  ascertain  the  tem- 
perature of  the  several  rays.  First  he  tried  the  up- 
per end  of  the  spectrum,  and  found  that  in  the  blue 
ray  the  mercury  marked  56°.  Then  passing  down- 
wards Humphry  was  overjoyed  to  see  the  quick- 
silver mount  as  he  proceeded  towards  the  middle, 
where,  in  the  yellow  ray,  the  instrument  indicated  a 
temperature  of  62°,  i.  e.  6°  higher  than  in  the  blue ; 
while  at  the  lower  end — at  the  extremity  of  the  red 
ray — -the  temperature  was  found  to  be  as  high  as 
79°,  i.  e.  17°  higher  than  it  was  in  the  yellow. 

There  was  then,  altogether,  as  much  as  33°  dif- 
ference between  the  heat  at  the  extreme  ends  of  the 
luminous  band — the  red  ray  being  upwards  of  half 
as  hot  again  as  the  blue  one — so  that  light  and  heat 
were  capable  of  being  separated  even  in  the  solar 
beams  themselves ; for  the  yellow  contained  the 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  163 

most  light  of  all,  and  yet  it  was  17°  colder  than  the 
extreme  verge  of  the  red  ray,  where  there  was  only 
a faint  luminous  blush  to  be  perceived. 

The  next  step  was  to  ascertain  the  circumstances 
regulating  the  reception  or  absorption  of  heat. 

Humphry  had  now  investigated  the  laws  which 
governed  the  radiation  or  emission  of  the  rays  of  heat 
from  bodies  at  an  elevated  temperature.  He  had 
ascertained  that  these  rays  not  only  emanated  from 
heated  substances  at  different  rates,  and  so  caused 
them  to  cool  down  more  or  less  rapidly,  but  that — 
though  their  tendency  was  to  proceed,  like  the  rays 
of  light,  in  a straight  line — they  were  capable  of  be- 
ing reflected  or  bent  back  by  certain  bodies  opposing 
their  progress,  and  that  in  such  cases  the  reflecting 
bodies  themselves  did  not  become  heated  by  them. 
Other  bodies,  again,  he  had  found  to  have  the  pow- 
er of  transmitting  the  rays  of  heat,  that  is  to  say,  of 
allowing  them  to  pass  through  their  substance  rath- 
er than  reflecting  or  driving  them  back  from  their 
surface ; and  such  transmitting  bodies,  moreover, 
were  likewise  scarcely  warmed  by  the  heat  that 
traversed  them.  Now  he  was  about  to  investigate 
the  conditions  that  determined  the  absorption  of  the 
heat-rays,  by  bodies  upon  which  they  fell  after  be- 
ing given  off  by  radiation  from  others  of  a higher 
temperature. 

The  lad’s  first  experiment  upon  this  subject  was 


164 


THE  WONDERS  OF  SCIENCE. 


to  blacken  the  surface  of  one  of  the  metal  mirrors 
that  he  had  previously  found  to  reflect  the  heat, 
without  being  itself  warmed  in  so  doing. 

The  result  proved  to  be  as  Humphry  had  antici- 
pated. The  mirror  no  longer  had  the  power  of  con- 
centrating the  heat  in  a focus,  at  a short  distance  in 
front  of  it : for  now,  instead  of  reflecting  the  rays  and 
remaining  cool  as  before,  it  absorbed  all  the  heat  that 
fell  upon  it,  and  became  itself  warmed  by  the  neigh- 
bouring radiator. 

The  same  effect  ensued  when  the  surface  of  the 
mirror  was  whitened  with  chalk,  and  the  same  again 
when  it  was  roughened,  or  scratched,  with  emery  pa- 
per : so  that  rough  and  dull  bodies  proved  to  be  bet- 
ter absorbers  of  heat — even  as  they  were  better  radi- 
ators— than  bright  or  polished  ones. 

Hence  there  appeared  to  be  some  connexion  be- 
tween the  radiating  and  absorbing  powers  of  differ- 
ent substances — those  which  cool  the  quickest  seem- 
ing to  be  capable,  also,  of  being  heated  in  the  short- 
est time. 

To  test  this  the  lad  placed  a blackened  and  a 
bright-polished  vessel  in  front  of  the  fire,  and  found 
that  the  thermometer  in  the  black  vessel  rose  much 
more  rapidly  than  did  that  in  the  bright  one. 

Humphry  then  availed  himself  of  these  two  ves- 
sels as  a means  of  testing  the  relation  between 
the  absorbing  and  radiating  powers  of  black  and 
bright-polished  surfaces.  Into  the  mouths  of  the 


THE  WONDERFUL  DIFFUSION  OF  HEAT,  165 

black  and  the  bright  tin  vessel  he  inserted  a ther- 
mometer, and  then  placed  between  them  one  of  the 
square  canisters  he  had  previously  employed,  and 
which,  it  will  be  remembered,  had  one  of  its  sides 
bright,  while  the  opposite  v one  was  coated  with 
lamp-black. 

Having  filled  the  middle  canister  with  boiling-hot 
water,  he  proceeded  first  to  note  the  radiating  and 
absorbing  effects  when  the  different  surfaces  were 
opposed  to  each  other.  On  arranging  the  middle 
canister  so  that  its  black  side  was  turned  towards 
the  polished  vessel  at  one  end,  and  its  polished  side 
to  the  blackened  vessel  at  the  other  end,  there  was 
no  effect  produced  upon  either  of  the  thermome- 
ters ; for  then  the  opposite  powers  of  the  different 
surfaces  exactly  balanced  each  other.  When,  howr- 
ever,  the  apparatus  was  so  adjusted  that  similar 
surfaces  were  opposed — that  is  to  say,  so  that  the 
blackened  side  of  the  canister  in  the  middle  was 
turned  towards  the  black  vessel,  and  the  bright- 
polished  side  to  the  bright-polished  vessel  — the 
thermometer  in  the  black  vessel  immediately  indi- 
cated a great  excess  of  heat ; for  then  not  only  was 
there  a good  radiator  opposed  to  a good  absorber , 
but,  on  the  other  side,  the  two  bright  surfaces 
were  facing  each  other — that  is,  the  bad  radiator 
was  turned  towards  the  bad  absorber — so  that  even 
the  little  heat  which  was  given  off  from  the  pol- 
ished side  of  the  canister  was  driven  back  again 


166 


THE  WONDERS  OF  SCIENCE. 


to  it  by  the  surface  of  the  neighbouring  bright 
vessel.  Hence  everything  favoured  the  radiation 
and  absorption  of  the  heat  on  the  one  side,  where 

i 

black  was  opposed  to  black,  and  prevented  it  on 
the  other,  where  metal  was  facing  metal ; and  thus 
the  great  elevation  of  the  thermometer  was  account- 
ed for.  •* 

As  it  was  now  winter  time  and  the  snow  lay 
thick  upon  the  earth,  Humphry  availed  himself  of 
the  circumstance  to  test  the  absorbing  powers  of 
different  colours.  For  this  purpose  he  took  a num- 
ber of  pieces  of  different  coloured  cloths,  and  placing 
them  at  mid-day  upon  the  snow,  so  that  the  sun’s 
rays  could  fall  directly  upon  them,  he  found  that 
the  dark  colours  sank  the  deepest  into  the  frozen 
mass  beneath,  while  the  lighter  hues  produced  scarce- 
ly any  thawing  effect,  and  the  white  remained  utter- 
ly inactive. 

The  same  result  was  obtained  by  means  of  col- 
oured glasses ; for  against  a window-pane  that  was 
covered  with  hoar-frost  the  lad  placed  some  pieces 
of  black,  red,  green,  and  yellow  glass,  and  the  con- 
sequence was,  that  the  ice  opposite  to  the  black  and 
red  pieces  was  melted  long  before  any  thawing  effect 
was  visible  upon  the  frozen  film  screened  by  the  oth- 
er colours. 

When  the  weather  grew  warm  Humphry  ob- 
tained another  very  curious  illustration  of  the  pow- 
er of  black  substances  to  absorb  the  heat  of  the 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  167 

sun’s  rays.  Having  filled  a glass  tube  with  spirits 
of  wine,  he  placed  it  in  the  focus  of  a lens,  a'nd 
found  that  the  solar  heat  traversed  the  transparent 
liquid  without  warming  it.  On  immersing  a small 
piece  of  charcoal,  however,  in  the  alcohol,  so  great 
was  the  absorptive  power  of  the  black  surface  that 
the  fluid  immediately  began  to  boil.  By.  the  same 
means,  too,  he  succeeded  in  raising  the  temperature 
of  water  to  the  boiling  point.  This  showed  that 
water,  as  well  as  spirits  of  wine,  was  a good  trans- 
mitter and  bad  absorber  of  heat ; that  is  to  say,  that 
the  rays  passed  freely  through  each  without  warm- 
ing either,  unless  some  substance  were  immersed  in 
the  liquid  in  order  to  detain  and  absorb  their  heat. 

Air,  on  the  other  hand,  the  boy  knew  to  have 
little  or  no  heat-absorbing  power;  for  the  rays 
emitted  by  a distant  hot  body  traversed  the  atmos- 
phere without  sensibly  raising  its  temperature.  He 
had  read,  too,  that  philosophers  had  calculated  that 
only  one-fifth  of  the  solar  heat  was  absorbed  in 
passing  through  1000  feet  of  the  air,  and  that  but 
one-third  of  the  entire  heat  of  the  sun  was  taken 
up  by  the  passage  of  the  beams  through  the  whole 
atmosphere. 

Humphry,  moreover,  sought  to  discover  whether 
the  sun’s  heat,  reflected  from  a mirror,  would  pro- 
duce the  same  effect  as  the  direct  solar  beams. 
Accordingly,  before  the  winter  passed  away,  he 
placed  two  pieces  of  blackened  card  upon  the  snow, 


168 


THE  WONDERS  OF  SCIENCE. 


at  a considerable  distance  apart.  One  of  these  lie 
left  exposed  to  the  direct  rays  of  the  sun,  while 
upon  the  other  he  caused  the  sun-beams  to  fall  in- 
directly, by  reflecting  them  from  a polished  metal 
surface.  The  black  card  that  was  submitted  to  the 
direct  solar  beams  sank,  after  a little  time,  deep 
into  the  snow,  While  the  frozen  mass  around — 
though  the  beams  fell  full  upon  it — was  but  slightly 
thawed.  With  the  black  card,  however,  upon  which 
the  sun’s  rays  were  reflected,  a precisely  opposite  re- 
sult ensued.  In  that  case  the  surrounding  snow  it- 
self was  the  first  to  melt,  while  the  blackened  sur- 
face seemed  to  have  been  deprived  of  its  power  of 
absorbing  heat,  and  remained  high  on  the  unthawed 
pile  beneath  it. 

Further,  Humphry  noticed  that  the  snow  which 
lay  near  the  trunks  of  trees,  or  wooden  posts,  melt- 
ed much  sooner  than  that  which  was  at  a distance 
from  them,  and  that  the  thawing  always  commenced 
at  the  side  facing  the  sun.  Hence  it  was  evident 
that  the  solar  heat,  after  being  either  reflected  or 
radiated  from  bodies  on  the  earth,  and  so  made  to 
fall  indirectly  upon  other  bodies,  was  rendered  capa- 
ble of  being  absorbed  by  substances  which,  like  snow, 
had  but  little  or  no  power  of  being  warmed  by  it 
directly. 

Why  this  should  be,  or  what  alteration  the  solar 
rays  underwent  in  impinging  upon  terrestrial  bod- 
ies, so  that  substances  which  before  absorbed  the 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  169 

sun’s  heat  with  difficulty  became  afterwards  more 
easily  warmed  by  it,  was  more  than  Humphry’s 
philosophy  could  explain — though  it  cost  him  many 
a day’s  hard  thinking  in  trying  to  account  for  the 
result. 

Having  now  investigated  the  conditions  which 
governed  the  diffusion  of  heat  from  a distant  point, 
Humphry  next  proceeded  to  inquire  into  the  cir- 
cumstances which  regulated  the  communication  of 
heat  to  bodies  in  contact  with  others  at  an  elevated 
temperature. 

This  constitutes  what  is  called  the  conduction  of 
caloric,  and  occurs  between  different  bodies,  or 
parts  of  the  same  body,  immediately  adjoining 
each  other.  The  communication  of  heat  by  con- 
duction is  a slow  process  compared  with  that  of 
radiation , which  is,  probably,  as  rapid  as  the  diffu- 
sion of  light  itself.  Philosophers  have  calculated, 
that  even  if  the  crust  of  the  earth  Avere  made  of 
cast-iron  (which  is  a much  better  conductor  than 
rocks  and  stones),  it  Avould  take  myriads  of  years 
to  transfer  the  heat  from  a depth  of  150  miles  be- 
low  the  surface  to  the  surface  itself ; whereas  by  ra- 
diation the  solar  heat  travels  from  the  sun  to  us  in 
8ijr  minutes. 

The  laAvs  which  regulate  the  communication  of 
caloric  to  distant  objects  are  similar  to  those  which  > 
Avould  ensue  if  the  heat  really  consisted  of  so  many 


170  THE  WONDERS  OF  SCIENCE. 

hot  particles  darted  out  from  the  heated  body  in  all 
directions ; and  colder  bodies  placed  in  the  neigh- 
bourhood of  heated  ones,  either  become  hot  in  the 
same  manner  as  they  would  if  such  particles  were 
positively  absorbed  by  them,  and  entered  into  their 
substance ; or  they  reflect  the  heat  to  other  bodies, 
while  they  themselves  are  unwarmed  by  it — as  if 
(according  to  the  hypothesis)  the  caloric  particles 
were  elastic,  and  had  the  power  of  bounding  off  from 
smooth  surfaces  interfering  with  their  progress ; or 
else  they  transmit  the  heat  rays,  as  if  the  imaginary 
particles  of  caloric  were  capable  of  freely  traversing 
certain  substances,  and  that,  also,  without  sensibly 
, raising  the  temperature  of  the  permeated  mass. 

But  all  bodies,  or  parts  of  bodies,  which  are  in 
immediate  contact  with  some  other  at  a higher  tern- 
perature,  become  themselves  warmed;  not  by  rays 
thrown  out  from  the  heated  mass,  but  by  conducting 
or  diffusing  the  heat  from  one  point  to  another,  and 
* so  disseminating  it  ultimately  throughout  their  whole 
substance. 

Humphry  was  thus  particular  in  impressing  upon 
his  mind  the  precise  difference  between  the  radia- 
tion and  conduction  of  caloric  before  entering  upon 
the  study  of  the  latter  process ; for  he  knew  that 
without  clear  and  distinct  views  upon  the  subject 
it  was  impossible  for  him  to  arrive  at  any  absolute 
knowledge. 

To  illustrate  the  gradual  progress  of  heat  by 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  171 


conduction , the  lad  took  a square  bar  of  iron,  about 
20  inches  long,  and  he  attached  to  the  under  side 
of  it  (by  means  of  a little  wax)  10  small  wooden 
balls,  so  that  they  were  about  2 inches  apart  from 
each  other.  Then  he  heated  one  end  of  the  bar  in 
the  flame  of  a lamp,  and  found  that  the  balls  fell 
from  under  it  , . - 

one  after  anoth-  | 

er,  as  the  heat 
found  its  way 

along  the  metal  and  melted  the  wax  below.  The 
arrangement  of  this  simple  and  instructive  experi- 
ment is  here  shown. 

The  next  step  was  to  learn  the  different  con- 
ducting powers  of  different  substances.  For  this 
purpose  Humphry  had  several  small  metal  cones 
made,  all  of  the  same  size ; one  of  these  was  of 

copper,  another  of  iron, 
a third  of  zinc,  a fourth 
of  tin,  a fifth  of  lead,  a 
sixth  of  marble,  and  a 
seventh  of  brick.  Then 
having  tipped  each  of 
them  with  a small  piece 
of  wax,  he  stood  them, 
all  a short  distance  apart 
from  each  other,  on  the 
metal  plate  at  the  top 
of  the  iron  stove  bv  which  Mr.  Borlase’s  sur- 


172 


THE  WONDERS  OF  SCIENCE. 


gery  was  heated.  The  result  was,  that  the  wax 
at  the  top  of  the  copper  cone  was  the  first  to 
melt.  Some  little  time  afterwards,  that  at  the 
apex  of  the  iron  began  to  liquefy ; and  soon  after 
the  iron,  that  upon  the  zinc  was  rendered  fluid  ; 
while,  shortly  following  the  zinc,  the  wax  on  the 
tin  commenced  trickling  down  the  sides.  A short 
interval  elapsed,  and  then  the  cerate  at  the  top 
of  the  lead  became  fluid.  Again  a lapse  of  a 
few  moments  occurred,  after  which  the  wax  with 
which  the  marble  cone  was  tipped  began  to  flow ; 
and,  last  of  all,  that  upon  the  piece  of  brick  was 
liquefied. 

The  different  conducting  powers  for  heat  among 
the  several  substances  employed  were  thus  made 
evident.  The  metals  were  more  capable  than  either 
marble  or  brick  of  diffusing  the  caloric  from  one 
part  of  them  to  another ; while  among  the  metallic 
substances  themselves  copper  was  proved  to  be  a 
much  better  conductor  thai  iron  ; iron,  again,  a lit- 
tle better  conductor  than  zinc  ; and  zinc,  too,  slight- 
ly better  than  tin.  Lead,  on  the  other  hand,  was 
the  worst  metallic  conductor  of  all. 

The  limited  means  of  the  young  experimentalist, 
however  (for  Humphry  was  obliged  to  seek  Mr. 
Tonkin’s  assistance  for  any  particular  apparatus  he 
required),  did  not  admit  of  his  testing  the  conduct- 
ing powers  of  either  gold  or  silver.  But  had  he 
done  so,  he  would  have  found  that  the  precious 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  173 


metals  were  much  better  conductors  than  any  other 
— gold  being  the  best  of  all,  and  silver  only  a little 
inferior  to  it.  Platinum , however,  was  a striking 
exception,  its  heat-conducting  power  being  only  a 
little  superior  to  that  of  iron. 

Humphry  after  this  sought  to  discover  what  would 
be  the  effect  if  he  placed  a good  conducting  metal 
in  connexion  with  a bad  one.  For  this  purpose  he 
employed  a short  curved  bar  of  copper ; and  having 
heated  it,  he  set  it  across  the  top  of  a small  leaden 
pillar  to  cool,  thus  : when,  to  his  utter  ^ 

astonishment,  a series  of  musical  sounds 
were  given  forth  as  the  copper  cooled, 
the  tones  now  rising  and  now  falling  like  those  of 
an  -ZEolian  harp. 

By  the  same  means  as  Humphry  had  employed 
for  testing  the  conducting  powers  of  the  metals,  he 
ascertained  that  ivood  was  a very  bad  conductor 
of  heat,  and  that  the  lightest  woods  were  the  worst. 
Charcoal , too,  he  found  to  have  but  little  power  of 
diffusing  the  heat  from  one  part  of  it  to  another. 
This  explained  to  the  boy  the  reason  why  a piece 
of  charcoal,  red-hot  at  one  end,  may  be  held — at  a 
short  distance  even  from  the  heated  part — without 
burning  the  fingers. 

Humphry  now  set  to  work  to  raise  to  a consid- 
erable temperature  several  pieces  of  such  substances 
as  he  had  ascertained  to  be  good  and  bad  conduct- 
ors, so  that  he  might  learn  what  effect  they  respect- 


">174 


THE  WONDERS  OF  SCIENCE. 


ively  produced  upon  the  touch  when  highly  heated. 
As.  he  had  anticipated,  the  bad  conductors — such  as 
the  wood  and  brick — could  be  handled  without  pain, 
whereas  the  good  conductors — like  the  metals — burnt 
the  fingers  immediately  they  were  brought  into  con- 
tact with  them. 

Pursuing  this  result,  the  lad,  eager  to  display  his 
knowledge  to  the  servant  of  the  house,  took  the  boil- 
ing kettle  from  the  kitchen  fire,  and,  to  the  amaze- 
ment of  the  maid,  allowed  the  sooty  bottom  of  it  to 
rest  upon  his  palm  ; for  the  crust  of  charcoal  with 
which  (by  long  usage)  the  vessel  had  "become  coated 
underneath — being  a non-conductor — prevented  the 
heat  of  the  boiling  water  within  being  communicated 
to  the  hand.* 

On  recounting  to  Mr.  Borlase  the  experiments 
he  had  performed  concerning  the  conduction  of 
heat,  Humphry  was  informed  by  that  gentleman 
that  it  was  painful  to  touch  good  conductors  like 
the  metals  when  they  were  heated  about  120°. 
Air,  however,  he  told  the  boy,  might  have  its 
temperature  raised  even  to  300°,  without  pro- 
ducing any  sense  of  burning ; adding,  that  some 
eminent  sculptors  had  large  ovens  in  connexion 
with  their  studios,  for  drying  the  moulds  they 


* Young  gentlemen  of  an  experimental  turn  are  cautioned 
against  attempting  the  same  feat ; for,  should  there  be  the  least 
part  of  the  metal,  at  the  bottom  of  the  kettle,  left  unprotected  by 
the  soot,  they  will  assuredly  experience  considerable  pain. 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  J 75 

employed  in  bronze  castings;  and  though  these  * 
places  were  often  heated  far  above  the  boiling 
point  of  water,  the  workmen  entered,  and  remained 
there  for  some  minutes  without  much  inconven- 
ience ; and  even  persons  unused  to  such  high  tem- 
peratures might  walk  in  and  out  of  the  ovens 
with  impunity,  though  to  such  any  attempt  to 
remain  occasioned  a difficulty  in  breathing  and 
a painful  sensation  about  the  eyes.  It  was  found 
necessary,  however,  under  such  circumstances,  to 
carefully  avoid  the  contact  of  any  good  conductor ; 
for  if,  while  in  the  heated  oven,  a piece  of  metal 

were  touched,  it  would  inevitably  burn — even  the 

/ 

coins  in  the  pocket  were  sufficient  to  produce  in- 
tense pain.  “ A story  is  told,”  he  continued,  “ of 
a person  who  once,  inadvertently,  entered  such  a 
place  with  his  spectacles  on,  and  these,  being 
mounted  in  silver,  soon  blistered  the  parts  of  his 
face  with  which  they  were  in  contact.  On  the 
other  hand,”  proceeded  the  surgeon,  “ it  has  been 
found  that  in  high  northern  latitudes,  where  the 
cold  is  sometimes  sufficiently  intense  to  freeze  mer- 
cury— though  this  requires  the  temperature  to  be 
72°  below  that  required  to  freeze  water — yet  even 
such  excessive  cold  may  be  borne  without  uneasiness, 
provided  the  air  be  tranquil,  and  the  persons  well 
clothed  in  good  non-conductors,  such  as  wool  and 
fur.  If,  however,  metallic  substances  be  touched  at 
this  low  temperature,  a sensation  like  that  of  burn- 


176  THE  WONDERS  OF  SCIENCE. 

ing  is  experienced,  and  the  part  quickly  becomes 
blistered.  “The  reason  of  this,”  the  doctor  con- 
cluded, “is,  that  the  heat,  being  as  it  were  free  to 
mo#ve  in  all  those  substances  which  are,  like  the  met- 
als, good  conductors  of  it,  is  readily  communicated 
to  us  by  such  substances  when  at  a higher  tempera- 
ture than  ourselves,  while  our  heat  is  as  readily  ab- 
stracted by  them  when  they  are  colder  than  we  are. 
Hence  good  conductors,  like  metals,  always  feel  cold- 
er to  the  touch  than  bad  conductors,  like  wood  or 
fur — even  though  these  latter  bodies  can  be  shown 
by  the  thermometer  to  be  of  the  same  temperature 
as  the  others.” 

Humphry’s  conversation  with  the  doctor  induced 
him  to  try  another  experiment,  illustrative  of  the 
conducting  power  of  wood  and  metal.  He  took  a 
small  rod  of  polished  brass,  about  a foot  in  length, 
and  stretching  a strip  of  writing-paper  tightly  over 
it  at  one  end,  he  tried  to  burn  the  paper  in  the 
flame  of  a lamp,  but  discovered  that  it  was  impos- 
sible even  to  scorch  it ; for  the  heat,  as  soon  as 
applied,  was  conducted  away  so  rapidly  along  the 
metal,  that  it  prevented  the  temperature  of  the  pa- 
per being  raised  sufficiently  to  char  it.  On  sub- 
stituting, however,  a smooth  piece  of  wood  for  the 
brass  rod,  he  found  that  the  paper  stretched  over 

i 

the  end  of  it  soon  began  to  scorch  in  the  flame,  and 
that  the  wood  itself  shortly  became  ignited  in  con- 
sequence of  its  bad  conducting  power,  which,  op- 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  177 

posing  the  diffusion  of  the  heat  along  it,  concen- 
trated the  effects  upon  the  spot  to  which  the  flame 
was  applied. 

After  this,  the  boy  began  to  turn  his  attention  to 
the  conducting  powers  of  liquids , rather  than  solids , 
with  which  he  had  previously  dealt. 

That  liquids  are  very  imperfect  conductors  of 
heat,  Humphry  made  out  in  the  following  manner : 
He  filled  a tumbler  with  water,  and  in  this  he 
placed  a piece  of  “ fusible  alloy,”  which  is  a com- 
position of  metals  melting  at  a temperature  below 
boiling  heat.  Then  a thin  copper  basin  was  made 
to  float  on  the  surface ; and  into  this  he  put  some 
pieces  of  red-hot  charcoal ; so  that,  after  a time, 
/the  stratum  of  water  at  the  top  of  the  tumbler  be- 
gan to  boil ; but,  even  though  the 
upper  part  of  the  liquid  was  at 
boiling-point,  so  slight  was  the 
power  of  the  water  to  conduct  the 
heat  from  one  part  of  it  to  anoth- 
er, that  the  stick  of  alloy,  which 
reached  within  an  inch  of  the  top, 
remained  wholly  unmelted  by  it. 

The  same  effect  was  found  to  ensue  with  heated 
oil,  though  this  the  lad  tried  in  a somewhat  dif- 
ferent manner.  In  a thin  glass  tube  a small  quan- 
tity of  water  was  frozen  by  plunging  it  into  a mix- 
ture of  salt  and  snow.  Then,  upon  the  lump  of  ice 
at  the  bottom  a small  quantity  of  oil  was  poured : 

M 


178 


THE  WONDERS  OF  SCIENCE. 


and,  lastly,  upon  the  oil  some  spirits  of  wine  was 

made  to  float.  The  tube  was 
now  held  over  the  chimney  of  a 
lamp,  and  the  spirit  made  to  boil 
until  the  whole  was  evaporated, 
when,  on  plunging  a thermom- 
eter into  the  oil,  it  was  found 
to  be  but  slightly  heated,  while 
the  ice  itself  had  undergone  no 
change,  but  remained  still  solid  at  the  lower  part  of 
the  tube. 

Next,  in  due  order,  came  the  conduction  of  heat 
by  gases  and  vapours;  and  of  this  Humphry  ob- 
tained a remarkable  illustration  in  a fact  which  he 
learnt  of  the  engineer  at  the  Wherry  Mine,  who 
told  the  lad  that  high-pressure  steam  did  not  burn, 
though  its  temperature  was  some  hundred  degrees 
above  that  of  steam  at  a low  pressure.  The  scald- 
ing effect  of  the  vapour  at  a low  pressure,  the  man 
informed  the  youth,  arose  from  the  small  particles 
of  hot  water  that  were  diffused  throughout  it,  and 
which,  indeed,  rendered  it  visible  in  the  air ; where- 
as in  high-pressure  steam  no  such  watery  particles 
existed,  and  the  vapour  was  consequently  not  only 
imperceptible  to  the  sight,  but,  being  a bad  conduct- 
or of  heat,  it  had  no  more  power  to  burn  than  so 
much  hot  air. 

Again,  that  gases,  in  a state  of  combustion,  are 
bad  conductors  of  heat,  Humphry  was  aware,  from 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  179 

having  repeatedly  passed  his  finger  through  the  flame 
of  a spirit-lamp  without  burning  it,  and  yet  the  tem- 
perature of  such  a flame  might  be  shown  to  be  many 
hundred  degrees  beyond  that  of  a piece  of  red-hot 
metal.  Air,  again,  he  knew  to  have  little  or  no 
conducting  power ; and  he  had  heard  from  Mr. 
Tonkin  that  in  Russia  and  other  cold  countries 
double  windows,  with  a stratum  of  air  between 
them,  were  used  to  prevent  the  heat  of  the  apart- 
ment being  carried  off.  So,  again,  in  furnaces, 
double  walls  with  a stratum  of  confined  air  in  the 
middle  are  employed  to  stop  the  egress  of  heat : 
even  as  in  ice-houses  the  same  means  are  adopted 
to  stay  the  ingress  of  it. 

The  diffusion  of  heat  by  the  process  of*  conduc- 
tion, however,  generally  occurs  among  solid  bodies, 
in  which  the  particles  are  more  or  less  firmly 
united ; but  liquids  and  gases  (where  the  particles, 
owing  to  the  want  of  cohesion  among  them,  are 
free  to  move)  mostly  became  warmed  by  a very 
different  process;  that  is  to  say,  the  heat  applied 
to  them  is  spread  from  one  part  to  another — not 
by  being  propagated,  as  in  solids,  from  one  fixed 
particle  to  that  which  is  next  to  it — but  by  the  mo- 
tion or  circulation  of  the  heated  particles  themselves , so 
that  each  in  its  turn  receives  a portion  of  the  heat 
applied,  and  then  giving  place  to  another  particle, 
the  whole  mass  ultimately  becomes  raised  to  one 


180 


THE  WONDERS  OF  SCIENCE. 


uniform,  temperature  by  the  direct  agency  of  the 
radiant  body,  rather  than  by  the  indirect  process  of 
transference  from  atom  to  atom  along  the  entire 
substance.  The  one  process  is  termed  the  conduc- 
tion of  heat,  the  other  the  convection  of  it ; and  while 
the  former  prevails  among  the  cohering  particles  of 
solid  bodies,  the  latter  generally  obtains  among  flu- 
ids whose  atoms  are  free  to  move. 

In  order  to  render  visible  this  same  circulation  of 
the  particles  of  fluids  while  in  a heated 
state,  Humphry  bruised  in  a mortar  a 
small  piece  of  amber,  and  then  having* 
filled  a glass  tube  with  water,  he  threw 
in  a few  pinches  of  the  powder,  which, 
being  nearly  of  the  same  specific  gravity 
as  the  liquid,  neither  sank  nor  floated  in 
it.  Then  applying  a gentle  heat  to  the 
centre  of  the  bottom  of  the  tube,  the  boy 
saw,  by  means  of  the  amber-dust  sus- 
pended in  the  fluid,  that  currents  im- 
mediately began  to  ascend  in  the  middle 
of  the  water,  and  to  descend  in  it  at  the 
sides  of  the  vessel — in  the  direction  of  the  darts  in 
the  above  engraving. 

If,  however,  he  heated  the  sides  of  the 
tube,  the  currents  were  found  to  take  a 
contrary  direction,  going  upwards  at  the 
sides  and  downwards  in  the  centre. 

On  continuing  the  heat,  Humphry  per- 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  181 

ceived  the  currents  to  become  more  and  more  rap- 
id, till  the  water  boiled,  and  when  the  whole  of  the 
liquid  had  acquired  an  uniform  temperature,  he  ob- 
served that  they  ceased  altogether.  He  then  en- 
deavoured to  ascertain  if  it  were  possible  to  pro- 
duce these  currents  in  a liquid  by  heating  it  at  the 
top,  but  the  boy  discovered,  on  apply- 
ing a spirit-lamp  to  the  upper  part  of 
the  tube,  thus — that  though  the  top 
of  the  water  was  made  to  boil,  and 
the  amber-dust  there  thrown  into  rap- 
id circulation,  the  particles  at  the  bottom  remain- 
ed unmoved,  the  fluid  below  being  undisturbed  and 
cold. 

The  reason  of  this  was  almost  self-evident.  The 
warm  water  was  lighter  than  the  cold,  and  there- 
fore rose  to  the  top  immediately  it  became  heated, 
while  the  cooler  and  heavier  portions  descended  to 
occupy  its  place.  Hence,  in  heating  the  tube  at 
the  bottom  the  current  was  observed  to  go  upwards 
in  the  middle  and  downwards  at  the  sides,  these 
being  kept  comparatively  cool  by  the  action  of  the 
external  air. 

Pursuing  this  subject,  Humphry  took  a large 
and  a small  Florence  flask,  and  into  the  mouth  of 
the  large  one  he  fitted  two  long  bent  glass  tubes,  by 
means  of  a perforated  cork  and  cement.  These,  to- 
gether with  the  large  flask,  were  filled  with  water 
and  then  made  to  dip  into  the  open  mouth  of 


182 


THE  WONDERS  OP  SCIENCE. 


the  smaller  flask,  which 
was  likewise  filled  with 
water,  but  tinged  a deep 
blue  with  indigo.  One 
of  the  tubes  was  arranged 
so  as  to  dip  only  about  half  an  inch  be- 
low the  surface  of  the  blue  liquid,  while 
the  other  descended  nearly  to  the  bottom 
of  it,  and  was  slightly  curved  upwards  at 
its  extremity.  The  arrangement  will  be 
readily  understood  by  reference  to  the 
annexed  engraving.  On  applying  the 
flame  of  a spirit-lamp  to  the  lower  flask, 
the  blue  liquid  was  seen  to  ascend  by  the 
tube  on  the  left  -side ; then  reaching  the 
large  flask  at  the  top,  it  there  circulated 
through  it,  in  the  direction  of  the  darts, 
and  descended  by  the  other  tube,  back 
again  to  the  small  flask  at  the  bottom. 
Thus  a perfect  circulation  was  seen  to 
be  kept  up,  and  the  heat,  by  means  of 
convection , carried  from  one  flask  to  the 
other. 

After  this  Humphry  sought  for  some 
means  of  rendering  the  currents  of  heated 
air  visible  in  the  same  manner.  For  such 
purpose  he  took  a large  glass  jar,  having  a 
wide  opening  at  the  bottom  and  a narrow 
one  at  the  top.  Into  the  upper  aperture 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  183 

he  inserted  a long  lamp-glass,  and  down  this  he 
placed  a diaphragm  of  card,  so  as  to  divide  the 
glass  chimney  into  two  channels.  Then  the  lad 
procured  a shallow  pan,  and  having  poured  a little 
water  into  it,  he  set  a piece  of  lighted  candle  in  it 
and  covered  it  over  with  the  jar  and  chimney,  so 
that  when  the  whole  was  duly  arranged  it  appeared 
as  here  shown.  Then 
having  lighted  a piece 
of  brown  paper  and 
blown  it  out  again,  he 
held  the  smouldering 
end  over  the  chim- 
ney, and  saw,  by  the 
curling  of  the  smoke 
from  the  paper,  that 
the  heated  air  from 
within  was  ascending 
the  lamp-glass  by  one 
side  of  the  diaphragm, 
and  descending  by  the 
other,  in  the  direction 
of  the  arrows  in  the 
illustration  ; whereas,  when  the  card-board  partition 
was  removed  from  the  chimney,  the  currents  ceased, 
and  the  light  wras  soon  extinguished. 

The  boy  applied  the  same  simple  means,  likewise, 
to  learn  the  direction  of  the  currents  of  air  on  open- 
ing the  door  of  a heated  apartment,  and  found,  by 


184 


THE  WONDERS  OF  SCIENCE* 


the  smoke  from  a piece  of  smouldering  paper,  that 
at  the  upper  part  of  the  door  the  heated  air  from 
within  was  rushing  outwards , and  at  the  lower  part 
the  cold  air  from  without  was  setting  inwards , whilst 
at  the  middle  scarcely  any  draught,  one  way  or  the 
other,  was  perceptible. 

This  naturally  turned  the  boy’s  attention  to  the 
subject  of  the  wind,  which  appeared  to  him  to  be 
merely  a vast  current  set  up  in  the  atmosphere  by 
the  heating  power  of  the  sun’s  rays.  He  had  no- 
ticed, too,  that,  shortly  after  sunrise,  a breeze  fre- 
quently sprang  up  at  sea  and  blew  towards  the  land, 
increasing  as  the  day  advanced,  and  declining  and 
ultimately  expiring  at  about  sunset ; whilst  in  the 
evening,  after  sundown,  a wind  often  arose  in  the 
opposite  direction— namely,  from  the  land  towards 
the  sea— and  lasted,  the  whole  of  the  night,  ceasing 
only  with  the  reappearance  of  the  sun. 

Humphry  was  therefore  anxious  to  discover  some 
experimental  means  of  reproducing  these  effects  on 
a small  scale. 

Having  procured  a large  shallow  milk-pan,  he 
filled  it  with  cold  water,  and  then  took  a metal 
“ hot-water  plate,”  and  having  poured  some  boiling 
water  into  this,  he  set  it  in  the  middle  of  the  pan, 
saying  to  himself  as  he  did  so,  “the  cold  water 
there,  in  the  outer  vessel,  represents  the  ocean, 
while  the  heated  metal  plate  in  the  centre  .stands 
for  an  island  warmed  by  the  rays  of  the  sun;  for 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  185 

the  land,  being  a better  absorber  of  heat  than  the 
sea,  will  have  its  temperature  raised  some  degrees 
higher  than  the  water  in  the  course  of  the  day.” 

This  done,  the  eager  boy  proceeded,  by  means  of 
the  smoke  from  a piece  of  smouldering  paper  as  be- 
fore, to  discover  the  direction  of  the  currents  that 
would  be  set  up  in  the  air  under  such  circumstances. 
As  he  held  the  smoking  paper  at  the  edge  of  the 
pan,  Humphry  was  delighted  to  see  the  white  fumes 
drawn  towards  the  hot  plate  in  the  middle,  or,  in 
other  words,  from  the  miniature  ocean  towards  the 
mimic  island  encompassed  by  it ; and  this  he  knew 
was  precisely  the  current  that  was  found  to  prevail 
throughout  the  day  in  tropical  countries. 


Then,  to  impress  the  phenomena  firmly  upon  his 


186 


THE  WONDERS  OF  SCIENCE. 


mind,  the  boy  drew  in  his  note-book  the  annexed  di- 
agrams, illustrative  of  the  currents  produced  in  the 
atmosphere  by  the  heating  of  the  earth  during  the  day , 
and  the  cooling  of  it  during  the  night.  “ But  if  the 


inequality  of  the  temperature  between  the  land  and 
the  sea  gives  rise  to  such  results,  how  much  great- 
er,” mused  the  boy  to  himself,  “ must  be  the  effect 
produced  by  the  difference  between  the  heat  of  the 
earth  at  the  equator— -where  the  average  tempera- 
ture is  said  to  be  80°— -and  at  the  poles,  where  it  is 
calculated  to  be  as  low  as  56°  below  zero,  the  differ- 
ence being  as  much  as  136° ! What  a vast  aerial 
current  must  be  set  up  by  such  means !” 

Then  the  lad  made  another  drawing,  illustrative 
of  the  effect  that  would  ensue  under  such  con- 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  187 

ditions,  and  he  set  above  it  a series  of  arrows  to 
show  the  direction  of  the  currents  that  would  be 
thus  induced  in  the  atmosphere.  For  the  air,  being 
heated  by  the  vertical  sun  at  the  tropics,  rises  there, 
as  it  does  up  a chimney,  while  the  colder  air  from 
the  northern  and  southern  hemispheres  glides  in 
from  below,  on  both  sides  of  the  equator,  to  supply 
the  place  of  that  which  has  been  made  to  ascend 
by  the  heat ; precisely  in  the  same  manner  as,  when 
the  fire  burns,  fresh  air  is  continually  rushing  in 
under  the  door  and  windows.  Then  the  heated  air, 
after  rising  to  a considerable  height  above  the  earth, 
at  length  flows  over,  as  it  were,  and  forms  in  the 


atmosphere  an  upper  current  from  the  equator  to 


188 


THE  WONDERS  OF  SCIENCE. 


the  poles,  where  it  becomes  cooled,  and  is  then 
drawn  down  to  supply  the  place  of  that  which  has 
been  drafted  from  the  colder  to  the  warmer  regions. 
“ But,”  said  the  boy,  as  he  surveyed  the  drawing, 
u according  to  this  the  winds  which  are  found  to 
prevail  in  the  tropics  should  blow  north  and  south; 
whereas  they  are  found  to  come  from  the  north-east 
and  south-east  quarters.” 

Humphry  puzzled  himself  for  a long  time  in  en- 
deavouring to  explain  the  phenomenon,  but  it  was 
more  than  his  philosophy  could  accomplish ; so  he 
had  to  consult  his  old  friend  Mr.  Tonkin  again,  and 
from  him  he  learnt  that  the  change  in  the  direction 
of  the  currents  is  due  to  the  motion  of  the  globe  and 
the  unequal  rates  at  which  different  parts  of  the 
earth’s  surface  revolve.  Consequently,  as  the  cur- 
rents of  air  which  set  in  towards  the  equator  from 
the  poles  come  from  parts  that  revolve  about  the 
axis  at  a much  slower  rate  than  the  equator  itself, 
they  hang  bach , or  drag , upon  the  surface,  in  a con- 
trary direction  to  the  rotation  of  the  earth  itself ; so 
that,  while  the  globe  turns  eastward,  they  acquire 
somewhat  of  a westerly  course,  and,  appearing  to 
come  from  the  opposite  quarter,  assume,  therefore, 
the  character  of  permanent  north-easterly  and  south- 
easterly winds. 

But  to  make  the  matter  clearer,  Mr.  Tonkin  ex- 
hibited the  following  illustration  to  the  boy,  in 
which  the  effect  of  the  earth’s  motion  in  changing 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  189 

the  direction  of  the  atmospheric  currents  is  imme- 
diately apparent. 


* The  old  gentleman,  however,  informed  Humphry 
that  there  are  other  terrestrial  currents  produced 
by  the  process  of  convection . In  the  ocean  the 
same  circulation  of  hot  and  cold  streams  is  found  to 
obtain ; for  the  sea,  warmed  by  the  heated  shores 
of  the  tropical  regions,  is  made  by  convection  to 
move  from  the  equator  like  a vast  river,  while  from 
the  poles  an  immense  current  of  colder  liquid  streams 
forward  to  supply  its  place.  For  the  same  reason 
as  was  before  explained  in  connexion  with  the  trade- 
winds,  the  polar  current,  having  a slower  rate  of 
rotatory  motion,  assumes,  on  reaching  the  equa- 
tor, a westerly  direction,  and  so  flows  in  one  broad 
stream  across  the  globe  ; then,  striking  against  the 
vast  continent  of  America,  it  divides  into  two  large 
streams.  One  of  these  flows  southward  down  the 


190 


THE  WONDERS  OF  SCIENCE. 


eastern  coast  of  Southern  America,  and  finally  en- 
ters the  Pacific  Ocean  through  the  Straits  of  Magel- 
lan. The  other  turns  northward,  enters  the  Gulf 
of  Mexico,  sweeps  round  the  coast  in  a powerful 
current  known  as  the  Gulf  Stream,  and  then  pro- 
ceeds along  the  Northern  American  shores  to  the 
coast  of  Newfoundland,  where  it  crosses  the  world 
again,  and  occasionally  extends  even  to  the  western 
shores  of  the  British  Isles. 

The  direction  of  these  oceanic  currents  is  indi- 
cated in  the  subjoined  chart : 


N 


S 


“ There  is,  however,”  continued  Mr.  Tonkin, 
“ another  great  heat-stream  traversing  the  earth, 
though  this  takes  place  within  the  crust  itself,  and 
is  due  more  to  conduction  than  convection , as  in  the 
other  cases.  For  philosophers  tell  us,  that  the 
daily  impressions  of  heat  which  the  earth  receives 


THE  WONDERFUL  DIFFUSION  OF  HEAT.  191 

from  the  sun,  follow  each  other  into  the  interior  of 
the  mass,  like  the  waves  which  start  from  the  edge 
of  a canal,  and,  like  them,  become  more  and  more 
faint  as  they  flow  on,  one  after  another,  till  they 
melt  into  the  general  level  of  the  internal  tempera- 
ture. The  parts  of  the  earth  near  the  equator,” 
added  the  old  man,  “ are  more  heated  by  the  sun 
than  other  parts,  and  on  this  account  there  is  a per- 
petual internal  conduction  of  heat  from  the  equatorial 
to  the  northern  and  southern  regions.  Then,  as  all 
parts  of  the  earth’s  surface  throw  off  heat  into  space 
by  radiation,  it  is  plain  that  at  the  poles,  where  the* 
surface  receives  but  little  warmth  from  the  sun,  a 
constant  waste  of  caloric  is  produced.  There  is 
thus  a perpetual  dispersion  of  heat  from  the  polar 
parts  into  surrounding  space,  which  is  supplied  by 
a perpetual  internal  flow  of  heat  from  the  equator 
towards  the  poles.  The  radiation  from  the  surface 
of  the  earth,”  Mr.  Tonkin  concluded,  “ has  its  limit 
in  the  temperature  of  the  planetary  space  in  which 
it  moves  (for  we  may  conceive  our  globe  to  be  like 
a heated  ball  cooling  down,  in  vacuo),  and  this  has 
been  calculated  to  be  not  more  than  56°  below  zero, 
— which  low  temperature,  indeed,  appears  to  be  at- 
tained in  the  long  absence  of  the  sun  in  a polar  win- 
ter.” 

The  poetic  boy  was  lost  in  wonder  at  the  mar- 
vellous results  to  which  his  investigations  had  led 
him,  and  his  mind  was  filled  with  a sense  of  sub- 


192 


THE  WONDERS  OF  SCIENCE. 


limity  at  the  thought  of  the  enormous  heat-tides  that 
are  continually  flowing  through  the  atmosphere,  the 
ocean,  and  the  solid  crust  of  the  earth  itself. 

“I’ll  work  it  all  out  myself,”  he  cried;  “ that  I 
will.  I’ll  not  I'est  until  I know  all  that  is  known 
of  Nature  and  her  wondrous  ways.” 


CHAPTER  VIII 


THE  WONDEKFXJL  EFFECTS  OF  HEAT. 

The  effects  of  heat  are  manifold. 

In  the  first  place,  an  increase  of  temperature  ex- 
pands or  enlarges  almost  all  bodies,  while  a decrease 
causes  them  to  contract  or  become  diminished  in 
bulk. 

Secondly.  Heat  changes  the  form  of  bodies,  con- 
verting solids  into  liquids,  and  liquids  into  vapours ; 
while  cold,  on  the  other  hand,  condenses  vapours 
into  liquids,  and  causes  liquids  again  to  solidify  or 
congeal. 

Thirdly.  Heat  causes  ignition;  that  is  to  say,  it 
changes  dark  opaque  substances  to  a bright  transpar- 
ent red,  rendering  them  capable  of  giving  out  light, 
when  their  temperatures  are  raised  to  a high  degree, 
and,  when  increased  to  the  highest  point,  causing 
them  to  become  even  white  in  the  fire,  and  then  en- 
dowing them  with  the  properties  of  the  solar  beams, 
so  that  their  rays  have  the  same  power  of  traversing 
plates  of  glass,  and  of  producing  chemical  changes, 
even  as  the  rays  of  the  sun  itself. 

N 


194 


THE  WONDEKS  OF  SCIENCE. 


Fourthly.  Combustion , or  the  burning  of  bodiesr 
with  the  evolution  of  flame,  is  another  effect  of 
heat.  There  is  also  a species  of  combustion  called 
sloiv  ( erema-causis  is  the  chemical  term  for  it),  which 
is  unaccompanied  with  flame — as  in  the  rotting  of 
wood  and  other  organic  tissues,  the  rusting  of  met- 
als, and  even  the  breathing  of  animals  and  ourselves. 
In  each  of  these  processes  there  is  the  same  combi- 
nation of  a combustible  body  with  the  oxygen  of  the 
atmosphere  — but  at  a much  sloiver  rate  — than  in 
the  more  rapid  and  energetic  forms  of  combustion ; 
and  hence  but  slight  increase  of  temperature  (if  any) 
is  discernible,  while  no  flames  or  luminous  gases 
that  are  perceptible  to  our  senses  are  evolved  under 
such  conditions. 

Fifthly.  Phosphorescence  is  likewise  produced  by 
heat.  During  combustion  and  ignition,  bodies  be- 
come temporarily  luminous ; but  in  states  of  what  is 
called  phosphorescence  they  are  permanently  so;  and 
there  are  many  substances — such  as  the  compact 
phosphate  of  lime,  the  dark-blue  kind  of  Derbyshire 
spar,  several  varieties  of  heavy  spar,  and  powdered 
quartz — which  acquire  the  property  of  shining  con- 
stantly in  the  dark  after  having  been  made  nearly 
red  hot. 

Sixthly.  Electricity  is  induced  by  heat ; for  it  has 
been  discovered  that  if  a bar  of  the  metal  called  an- 
timony be  heated  at  one  end,  while  the  other  is  kept 
cool,  an  electric  current  ensues.  ' 


THE  WONDERFUL  EFFECTS  OF  HEAT.  195 

Lastly.  Heat  promotes  both  vegetable  and  animal 
life.  For  not  only  is  intense  cold  destructive  of  or- 
ganic existence,  but  the  increased  warmth  of  the 
summer  invariably  calls  into  being  an  infinite  num- 
ber of  plants,  flowers,  insects,  and  the  many  forms 
of  organised  nature  that  give  variety  and  grace  to 
the  earth.  Moreover,  heat  produces  in  ourselves, 
and  other  sentient  animals,  a feeling  of  warmth, , and 
the  absence  of  it  a sensation  of  cold ; by  which  we 
are  enabled  to  measure — though  hardly  with  perfect 
accuracy — the  different  changes  of  temperature  oc- 
curring in  the  substances  around  us,  and  also,  by  the 
agreeable  impression  which  we  derive  from  warmth, 
induced  to  seek  that  degree  of  heat  which  is  best 
fitted  for  the  promotion  of  our  health  and  develop- 
ment of  our  faculties. 


Humphry  began  by  studying  the  laws  which  reg- 
ulate the  expansion  of  bodies  under  the  three  differ- 
ent forms  in  which  they  exist  in  nature,  viz.  solids , 
liquids , and  gases  or  vapours.  To  determine  the  ex- 
pansion of  different  solids,  the  youth  procured  short 
bars  of  the  several  substances  upon  which  he  had 
decided  to  experiment.  The  bars  were  all  of  the 
same  length  and  thickness,  and  were  accompanied 
with  a gauge,  which  measured  their  dimensions  at 
ordinary  temperatures. 

The  following  diagram  illustrates  the  apparatus 


196 


THE  WONDERS  OF  SCIENCE. 


employed.  The  first  step  was  to 
test  the  length  and  breadth  of 
each  bar  that  was  to  be  used. 
This  was  performed  first,  by  plac- 
ing it  in  the  gap  at  the  upper  part 
of  the  gauge,  and  seeing  whether 
it  exactly  fitted  between  the  notch- 
es; and  secondly,  ascertaining  whether  it  was  pre- 
cisely of  the  same  diameter  as  the  hole  at  the  bot- 
tom part  of  the  plate.  This  done,  the  bars  were 
successively  plunged  into  hot  water,  when,  on  ap- 
plying them  once  more  to  the  gauge,  they  were 
found  to  be  so  much  enlarged  in  all  their  dimen- 
sions that  it  was  impossible  to  make  them  pass 
through  either  of  the  apertures.  After  this  they 
were  severally  cooled  down,  by  immersion  in  a mix- 
ture of  snow  and  salt,  to  the  temperature  of  the 
freezing-point  of  water,  when  they  were  discovered 
to  have  considerably  contracted  in  bulk ; so  that  they 
could  be  passed  through  both  of  the  openings  with 
perfect  ease. 

It  was  by  such  means  Humphry  ascertained 
that  different  solids  possessed  different  degrees  of 
expansibility,  and  that  metals  are  more  suscep- 
tible of  change  of  bulk  than  other  solid  bodies. 
Each  solid,  however,  was  found  to  have  a rate  of 
dilatation  peculiar  to  itself.  Lead , for  instance, 
when  heated,  from  the  freezing  to  the  boiling-point 
of  water,  was  discovered  by  measurement  to  have 


THE  WONDERFUL  EFFECTS  OF  HEAT.  197 

expanded  one-350th ; iron,  one-800th;  and  glass, 
one-lOOOth. 

Platinum,  however,  was  found  to  be  less  expans- 
ible than  iron,  and  copper  more  so.  Silver,  on  the 
other  hand,  was  more  expansible  than  copper,  while 
tin  was  more  so  than  silver ; lead,  again,  more  than 
tin,  and  zinc  even  more  than  lead : so  that  glass  was 
proved  to  be  less  capable  of  being  increased  in  bulk 
by  heat  than  the  metals  ; whilst,  among  the  metals 
themselves,  platinum  was  ascertained  to  be  the  least 
expansible,  and  zinc  the  most  so. 

On  talking  over  these  matters  with  Mr.  Borlase, 
the  doctor  told  Humphry  that  the  expansion  of  met- 
als was  a matter  of  considerable  importance  in  many 
arts.  “ For  instance,”  said  the  gentleman,  “ coopers 
put  the  iron  hoops  upon  their  casks  in  a heated  state, 
so  that  they  may  gradually  contract  on  cooling,  and 
firmly  bind  the  staves  together.  With  the  same  view 
the  wheelwright  heats  the  tire  of  his  wheel,  in  or- 
der that  it  may,  as  it  cools,  press  strongly  upon  the 
i felly,’  or  circumference ; and,  for  the  same  reason, 
the  plates  of  large  boilers  are  united  with  red-hot 
rivets,  which,  during  their  contraction  on  cooling, 
draw  the  sheets  of  metal  closely  and  securely  together. 

“In  the  iron  bridge,”  continued  the  doctor, 
“ which  was  constructed  over  the  Severn  in  Shrop- 
shire, when  I was  a lad,  it  has  been  found  that  the 
arches  are  nearly  one  inch  longer  in  summer  than 


198 


THE  WONDERS  OF  SCIENCE. 


they  are  in  winter ; so  that,  if  due  allowance  had 
not  been  made  for  the  expansion  of  the  metal,  the 
stone  piers,  on  which  the  arches  rest,  must  have 
given  way  to  the  pressure  long  before  this.  The 
same  allowance  for  expansion,  Humphry,  has  to  be 
made  in  the  clamping  together  of  stones  in  the  con- 
struction of  church  steeples ; for  the  changes  of  bulk 
which  occur  in  metals  at  different  temperatures, 
though  comparatively  small  in  amount,  take  place 
with  irresistible  force.” 

The  perpendicularity  of  the  walls  of  the  Muse- 
um of  Arts  and  Manufactures,  in  Paris,  it  may  be 
added,  were  restored  by  Molard,  upon  the  same  prin- 
ciple. In  consequence  of  the  weight  of  the  roof,  the 
walls  were  bulging  outward,  and,  in  order  to  straight- 
en them,  iron  rods  were  laid  across  the  interior  of 
the  building,  their  ends  being  made  to  project  through 
the  brickwork  outside.  These  rods  were  then  heat- 
ed, and,  when  in  an  expanded  state,  a strong  iron 
plate  was  passed  over  each  end  of  them,  and  screwed 
firmly  up  against  the  exterior  of  the  walls.  As  the 
rods  cooled,  they  naturally  contracted,  and  drew  the 
walls  somewhat  nearer  together.  The  bars  were  aft- 
erwards again  elongated  by  heat,  and  again  screwed 
up  previous  to  their  contraction ; and  so,  by  a repeti- 
tion of  the  process,  the  walls  were  gradually  brought 
to  a perpendicular  position. 

Humphry  was  delighted  with  the  ingenious  ap- 
plications of  the  expansion  and  contraction  of  metals 


THE  WONDERFUL  EFFECTS  OF  HEAT.  199 

by  heat  and  cold,  and  Mr.  Borlase,  observing  the 
interest  he  took  in  the  subject,  proceeded  to  explain 
to  him  how,  by  the  same  principle,  the  alterations 
in  the  length  of  the  pendulum  of  a clock  were  “com- 
pensated,” and  the  instrument  so  made  to  vibrate 
seconds  at  all  seasons.  For  a pendulum  to  beat 
exactly  sixty  times  a minute,  he  told  the  boy,  it 
was  necessary  that  it  should  be  a fraction  more 
than  39  inches  long,  in  the  latitude  of  London. 
“ If,  however,  the  pendulum  be  made  of  metal,”  he 
said,  “ it  will  be  liable  to  be  longer  in  summer  and 
shorter  in  winter ; so  that  the  clock  will  be  slow 
in  the  warm  weather  season  and  fast  in  the  cold  : for 
when  the  bob  is  let  down  the  one- 100th  part  of  an 
inch  the  clock  loses  10  seconds  in  24  hours,  and  a 
change  of  temperature  equal  to  30°  (which  is  nearly 
the  difference  between  summer  and  winter,  in  our 
climate),  will  alter  the  length  of  the  pendulum-rod 
about  one-5 000th  part,  and  so  occasion  an  error  in 
the  rate  of  going  of  8 seconds  a day. 

“To  counteract  the  expansions  of  the  metal  rod 
of  the  pendulum,”  continued  his  preceptor,  “ there 
are  many  ingenious  contrivances.  The  simplest  of 
these,  perhaps,  is  as  follows : A compound  bar  of 
two  differently  expansive  metals,  such  as  steel  and 
brass,  is  formed  by  rivetting  or  soldering  the  two 
metals  together ; for  if  such  a bar,  with  the  brass 
up2)ermost,  be  placed  upon  a heated  plate,  it  will  be 
found  to  warp  or  curve  cloivnwards , in  consequence 


200 


THE  WONDERS  OF  SCIENCE* 


V, 


of  the  expansion  of  the  brass  being  greater  than  that 
of  the  steel.  If,  however,  on  the  other  hand,  the 
compound  bar  be  placed  on  a plate  cooled  down  by 
a mixture  of  snow  and  salt,  it  will  be  found  to  warp 
or  curve  upwards , because  the  brass  will  contract  the 
more  with  the  cold.  Now,  if  two  such  compound 
bars,  with  the  most  expansible  metal  at  top,  be  placed 
at  the  upper  part  of  a pendulum-rod,  one  on  either 
side  of  it,  and  firmly  fixed  at  one  end,  they  will,  as 
they  warp  upwards  or  downwards,  tend  to  shorten 
the  pendulum-rod  when  it  becomes  lengthened  by 
the  heat,  and  to  lengthen  it  when  it  becomes  con- 
tracted by  the  cold. 

To  make  this  more  readily  intelligible  to  Hum- 
phry, the  doctor  exhibited  to  him  the  following  ern 
gravings : 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


201 


“Let  us  now,”  said  Mr.  Borlase,  as  he  placed  his 
finger  on  the  centre  drawing,  “suppose  the  pendu- 
lum, with  the  compensation-bars  perfectly  horizon- 
tal, to  be  vibrating  seconds  at  a temperature  of  60°, 
and  that,  some  few  months  afterwards,  the  heat  rises 
to  80°  ; in  such  a case,  of  course,  the  pendulum-rod 
would  be  elongated  by  the  heat , and  the  longer  the  rod 
the  slower  the  vibrations,  so  that  it  would  then  vi- 
brate less  than  sixty  times  in  the  minute.  The  ef- 
fect of  the  increase  of  temperature,  however,  on  the 
compensation-bars  (the  most  expansible  metal  being 
uppermost),  would  be  to  warp  them  downwards  (as 
shown  in  the  left-hand  drawing),”  said  the  doctor, 
pointing  to  the  illustration,  “and  thus  they  would 
shorten  the  pendulum-rod  as  much  as  the  heat  had 
lengthened  it.  In  cold  weather,  however,  Hum- 
phry, the  metal  rod  of  the  pendulum  would  be  di- 
minished in  length;  but  then  the  compensation-bars 
would  warp  upwards , and  so  tend  to  elongate  it,  to 
the  same  extent  as  it  had  been  contracted  by  the 
cold  (as  may  be  seen  on  reference  to  the  picture  on 
the  right  hand).” 

The  next  day  Humphry  was  busy  making  experi- 
ments concerning  the  expansion  of  liquids.  He  first 
took  a large  thermometer  tube  and  poured  into  it  a 
sufficient  quantity  of  spirits  of  wine  to  fill  the  bulb 
at  the  bottom  and  make  the  fluid  rise  some  few  inch- 
es in  the  stem  above.  Then,  having  marked  upon  the 


202 


THE  WONDERS  OF  SCIENCE. 


glass  with  a file  the  level  at  which  the  spirit  stood 
at  an  ordinary  temperature,  the  boy  plunged  the  in- 
strument into  a vessel  of  boiling  water,  and  immedi- 
ately beheld  the  liquid  rise  in  the  tube  till  it  stood 
several  inches  above  its  former  level.  After  this  he 
immersed  the  tube  in  a mixture  of  snow  and  salt, 
and  found  the  liquid  contract,  so  that  it  fell  in  the 
stem  almost  down  to  the  bulb.  On  removing  the 
instrument,  however,  the  fluid  immediately  com- 
menced rising  again,  and  so  pleased  was  the  youth 
with  the  motions  that  he  repeated  the  experiment 
over  and  over  again,  being  not  a little  delighted  to 
perceive  that  each  time,  as  he  plunged  the  instrument 
into  the  hot  or  cold  bath,  the  spirit  invariably  rose 
or  fell  to  precisely  the  same  place  in  the  tube. 

To  measure  the  different  rates  of  expansion  among 
different  liquids,  the  young  chemist  provided  himself 
with  a long  and  narrow  glass  tube,  which  was  grad- 
uated into  cubic  inches,  and  into  this  he  poured  a 
certain  quantity  of  the  liquid  he  wished  to  experi- 
ment upon.  Then  plunging  the  graduated  tube  into 
the  snow-and-salt  mixture,  he  noted  the  precise  vol- 
ume of  the  fluid  at  that  temperature ; after  which 
he  immersed  it  in  a vessel  of  boiling  water,  and  then 
noted  again  how  many  cubic  inches  it  occupied  in 
the  tube  at  the  higher  temperature ; so  that  the  dif- 
ference told  him  how  much  the  liquid  had  been  ex- 
panded between  32°  and  212°,  or  the  freezing  and 
boiling  point  of  water. 


THE  WONDERFUL  EFFECTS  OF  HEAT.  203 

It  was  thus  the  lad  ascertained  that  9 measures 
of  spirits  of  wine  at  32°  become  expanded  into  10 
measures  at  212°,  and  9 measures  of  strong  aqua- 
fortis also  become  10,  between  the  same  extremes 
of  temperature.  Again,  12  measures  of  olive  oil 
are  increased  into  13,  while  14  of  ether  and  the 
same  quantity  of  oil  of  turpentine  swell  each  into 
15,  with  the  like  increase  of  heat.  Then  17  meas- 
ures of  oil  of  vitriol,  at  the  freezing-point  of  water, 
are  dilated  into  18  at  the  boiling-point,  and  22§ 
measures  of  water  are  increased  to  23f  within  the 
same  range  of  temperature,  while  55^  of  quicksilver 
become  56^  when  similarly  treated;  consequently 
spirits  of  wine  is  no  less  than  6 times  more  expansi- 
ble than  quicksilver,  so  that  in  the  depth  of  winter 
100  pints  of  spirits  of  wine  are  dilated  into  105  in 
the  height  of  summer. 

While  making  his  experiments,  however,  as  to  the 
rate  of  expansion  in  liquids,  the  boy  had  been  aston- 
ished to  perceive,  when  the  tube  contained  water, 
that,  on  placing  it  in  the  mixture  of  snow  and  salt, 
the  liquid,  as  it  was  cooled  down,  continued  to  shrink 
till  it  had  attained  the  temperature  of  about  40° ; 
and  then,  instead  of  contracting  any  farther  (as  was 
the  case  with  other  liquids  till  they  froze),  it  began 
to  expand  slowly , and  kept  rising  in  the  tube  until  it  con- 
gealed. He  noticed,  too,  that,  when  the  water  was 
at  its  freezing  point,  or  32°,  it  was  of  the  same  bulk 
as  it  was  at  48°  ; so  that  it  expanded  just  as  much 


204 


THE  WONDERS  OF  SCIENCE. 


for  the  8°  below  40°  as  it  had  contracted  in  the  8° 
above  that  point. 

Humphry  then  tried  another  experiment  illustra- 
tive of  this  remarkable  property  of  water.  Having 
produced  two  cylindrical  glass  vessels,  he  surrounded 
one  of  them  at  the  bottom  with  a circular  tin  tray, 
that  fitted  closely  to  the  exterior  of  the  cylinder,  and 
affixed  to  the  other  a similar  tray,  but  this  he  placed 
at  the  upper,  instead  of  the  lower  part  of  the  cylin- 
der as  before — in  the  manner  represented  in  the  sub- 
joined engraving: 


A thermometer  then  having  been  placed  in  each 
of  the  glass  vessels,  they  were  respectively  filled 
with  water  at  50°,  while  a freezing  mixture  of 
pounded  ice  and  salt  was  placed  in  each  of  the 
trays. 


THE  WONDERFUL  EFFECTS  OF  HEAT.  205 

After  the  temperature  of  the  whole  of  the  water 
in  both  vessels  had  been  reduced  to  40°,  it  was 
found  by  the  thermometer  in  the  vessel,  with  the 
freezing  mixture  at  the  top , that  the  cooling  effect 
would  not  proceed  downwards,  hut  was  limited  to 
the  surface , where  the  water  ultimately  froze ; for 
the  ice-cold  water  being  lighter  than  the  water  be- 
low at  40°,  necessarily  floated  like  oil  upon  the  sur- 
face. In  the  other  cylinder,  however,  where  the 
cold  was  applied  at  the  lower  rather  than  the  upper 
part  of  the  water,  the  effect  was  very  different ; for 
there,  the  liquid  becoming  lighter,  as  its  tempera- 
ture sank  below  40°,  ascended , whilst  the  warmer 
and  heavier  water  at  the  top  descended , until  it  was 
cooled,  and  so  expanded  in  its  turn ; and  thus  the 
whole  of  the  liquid  was  ultimately  reduced  to  the 
freezing-point ; whereas  in  the  other  cylinder  this 
effect  was  limited  to  the  surface  only.  Humphry 
now  could  see  the  reason  why  lakes  and  ponds  froze 
only  on  the  surface,  and  why,  on  breaking  the  ice 
(as  he  had  repeatedly  done  when  out  snipe-shooting 
with  his  uncle,  Leonard  Millett),  the  water  under- 
neath was  always  found  to  be  warmer  than  the  air 
above. 

The  lad  had  now  but  to  investigate  the  rate  of 
expansion  among  aeriform  bodies , or  gases , to  com- 
plete this  part  of  the  subject. 

Accordingly,  he  took  the  thermometer  tube  he 


206 


THE  WONDERS  OP  SCIENCE. 


had  before  used,  and  placed  it,  with  its  open  end, 
downwards,  in  a glass  of  water,  thus : 


The  tube  was  of  course  filled  with  air,  so  he  ap- 
plied his  palm'  bo  the  bulb,  and  found  the  heat  of 
the  hand  sufficient  to  expand  the  air  within,  and 
drive  a stream  of  bubbles  up  through  the  water. 
On  removing  the  source  of  heat,  however,  the  vol- 
ume of  air  began  to  contract,  and  the  liquid  to 
mount  in  the  tube,  so  that  he  could  see  by  the 
height  the  water  rose  in  the  stem  the  amount  of  ex- 
pansion which  the  air  had  undergone. 

Humphry  then  proceeded  to  ascertain  the  amount 
of  expansion  produced  in  a given  quantity  of  air, 
when  heated  from  the  freezing  to  the  boiling  point 
of  water,  and  discovered  that  100  cubic  inches  of 


THE  WONDERFUL  EFFECTS  OF  HEAT.  207 

air  at  32°  become  dilated  to  137J  cubic  inches  at 
212°.  Air,  therefore,  at  the  freezing-point,  expands 
one-480th  for  every  degree  of  heat  that  is  added  to 
it;  so  that  480  cubic  inches  at  32°  become  481  at 
33°,  and  482  at  34°,  and  so  on,  the  volume  expand- 
ing one  cubic  inch  with  each  additional  degree  of 
heat.  A volume  of  air,  therefore,  at  32°  would  be 
doubled  at  480°,  and  tripled  at  960°,  the  latter  tem- 
perature being  that  of  a dull-red  heat. 

Steam,  and  other  vapours,  when  heated  by  them- 
selves, are  subject  to  the  same  law  of  expansion  as 
air. 

But  although  the  expansion  produced  in  aeriform 
bodies  by  heat  is  great  in  amount,  the  actual  force 
which  is  thus  developed  is  small  when  compared 
with  that  of  solids  and  liquids  under  the  same  cir- 
cumstances. This  is  owing  to  the  extreme  elastici- 
ty of  aeriform  bodies  ; so  that,  although  air  becomes 
tripled  in  volume  at  a red  heat,  vessels  are  easily 
found  capable  of  sustaining  the  pressure  of  the  ex- 
panded fluid.  It  is  only  when  a portion  of  liquid  is 
present,  so  that  volume  after  volume  of  vapour  is 
added  to  those  already  generated — as  in  the  produc- 
tion of  steam — that,  on  resisting  the  expansion,  the 
pressure  becomes  enormous,  and  mounts  up  to  a dan- 
gerous point.  . 


CHAPTER  IX. 


THE  WONDERFUL  EFFECTS  OF  HEAT- — (continued). 

“ But  heat,”  said  Humphry  to  himself,  as  he  re- 
viewed his  previous  experiments,  “not  only  expands 
the  bulk  of  different  bodies,  but  it  changes  their  form , 
rendering  certain  solids  liquid,  and  converting  liquids 
into  vapours.  Let  us  see  now  what  occurs  during 
such  changes.” 

Accordingly,  the  youth  proceeded  to  pound  some 
ice,  and  to  cool  it  down  in  a tumbler  by  means  of  a 
freezing  mixture  to  the  temperature  of  zero.  The 
tumbler  was  then  inserted  in  a bath  of  tepid  water, 
the  temperature  of  which  was  maintained,  by  an 
argand-lamp  beneath  it,  constantly  at  60°.  A ther- 
mometer having  been  plunged  in  the  ice,  the  quick- 
silver was  observed  to  mount  rapidly  in  the  tube 
until  it  reached  32°,  when  the  ice  began  to  liquefy. 
But,  though  another  thermometer  in  the  water-bath 
showed  that  the  liquid  there  was  still  60°  hot — the 
same  temperature,  indeed,  as  when  the  ice  was  first 


THE  WONDERFUL  EFFECTS  OF  HEAT.  209 

immersed  in  it — nevertheless  the  thermometer  in  the 
tumbler  remained  stationary  at  32° — the  freezing- 
point.  Nor  did  it  begin  to  rise  until  the  whole  of 
the  ice  .was  melted  ; after  which  it  mounted  gradu- 
ally, and  ultimately  settled  at  60°,  the  temperature 
of  the  surrounding  water. 

Humphry  was  astonished  at  the  effect.  “ Why 
did  the  thermometer,”  he  asked  himself,  “ remain 
fixed  at  the  freezing-point  until  the  whole  of  the 
ice  was  melted?  The  heat  from  the  surrounding 
water  must  have  been  entering  the  ice  as  much 
when  it  began  to  dissolve,  as  it  did  before  the 
thawing  occurred,  or  even  afterwards.  How,  then, 
came  it  that  the  thermometer  was  not  affected  by 
it?” 

The  eager  boy  was  so  puzzled  with  the  mystery, 
that  he  could  not  rest  till  he  had  tested  the  result  by 
another  experiment. 

Having  procured  two  small  glass  globes,  he  filled 
them  both  with  the  same  quantity  of  water.  The 
liquid  in  one  he  froze,  and  that  in  the  other  he  cooled 
down  to  33°,  so  that  it  might  be  as  near  as  possible 
to  the  temperature  of  the  first,  without  being  solid. 
When  the  ice  in  the  one  globe  had  just  begun  to 
melt,  and  the  thermometer  in  that  vessel  marked 
32°,  the  two  globes  were  plunged  into  a water-bath, 
the  temperature  of  which  was  kept  at  47°  through- 
out the  experiment. 


O 


210 


THE  WONDERS  OF  SCIENCE. 


The  vessels,  therefore,  were,  as  near  as  possible, 
under  similar  conditions  of  temperature,  within  and 
without,  and  with  similar  contents — except  that  the 
one  contained  ice,  and  the  other  water. 

The  progress  of  the  heating  was  then  noted. 

In  the  globe  which  contained  the  water , Humphry- 
found  the  thermometer  rose  in  half  an  hour  to  40°. 
In  the  globe,  however,  which  contained  the  ice , no 
less  than  10-1  hours  elapsed  before  the  whole  was 
melted,  and  the  temperature  of  the  resulting  liquid 
raised  to  40°,  like  the  other ; so  that  the  rate  of  heat- 
ing in  the  ice-vessel  was  2 1 times  slower  than  in  that 
which  held  the  water. 

“How  can  this  be?”  mused  the  boy -philoso- 
pher. “ The  actual  amount  of  heat  received  by 
the  two  must  have  been  uniform  during  the  whole 
time,  and  yet  the  ice  took  10-^-  hours  to  have  its 
temperature  raised  to  40°,  while  the  ice-cold  water 
needed  only  an  hour  to  acquire  the  same  heat. 
How  extraordinary !”  he  inwardly  exclaimed ; 
“what  can  be  the  cause  of  it?  For,”  said  the  lad, 
as  he  jotted  the  figures  down  in  his  note-book,  “ the 
water  in  the  globe  had  its  temperature  raised  7° 
in  half  an  hour,  consequently  that  must  have  been 
the  rate  at  which  the  warmer  liquid  in  the  external 
bath  was  giving  out  its  heat  to  the  two  globes. 
Accordingly,  in  10-lr  hours  it  must  have  given  10^ 
times  7°,  or  147°  in  all,  to  the  one  containing  the 


THE  WONDERFUL  EFFECTS  OF  HEAT.  211 

ice.  Consequently  the  ice  required  140  more  degrees 
of  heat  to  raise  its  temperature  to  40°  than  the  wa- 
ter did.” 

Humphry  still  doubted  the  accuracy  of  his  con- 
clusions ; for  they  were  so  marvellous  and  unex- 
pected by  him,  that  he  sat  for  a long  time  con- 
sidering by  what  experiment  he  could  bring  the 
matter  to  a positive  test.  “If,”  he  inwardly  ex- 
claimed, “the  ice  really  received  140°  more  heat 
than  the  water,  what  became  of  them'?  The  two 
were  each,  in  the  end,  of  the  same  temperature ; 
and  the  thermometer  didn’t  show,  nor  could  I 
feel,  that  the  one  had  imbibed  more  heat  than  the 
other.” 

Presently  the  boy  started  to  his  feet,  for  a sudden 
thought  had  struck  him.  He  would  take  12  oz.  of 
pounded  ice,  and  upon  this  he  would  pour  the  same 
weight  of  hot  water,  at  a temperature  of  172° ; so 
that  the  difference  between  the  heat  of  the  ice  and 
that  of  the  water  would  be  172° — 32°,  or  exactly 
140°,  and  this  was  precisely  the  quantity  of  heat 
that  the  ice  in  the  previous  experiment  had  received 
over  and  above  the  water. 

Humphry  wondered  again  and  again,  as  he  pre- 
pared the  experiment,  what  the  result  would  be ; 
and  when  he  mixed  the  warm  water  with  the  ice, 
he  was  overjoyed  to  find  that  the  temperature  pro- 
duced was  only  32° — the  same  as  that  of  the  pound- 
ed ice  itself.  Hence  it  was  plain  the  water  had  lost 


212 


THE  WONDERS  OF  SCIENCE. 


exactly  140°  of  its  heat,  and,  moreover,  that  these 
had  entirely  disappeared , since  the  temperature  of  the 
colder  substance  remained  the  same  as  at  the  outset 
of  the  experiment. 

Then  came  the  question — What  had  become  of 
the  lost  heat1?  Where  had  it  gone?  What  effect 
had  it  produced? 

There  was  hut  one  answer ! and  this  Humphry 
was  not  long  in  divining.  The  heat  which  had  dis- 
appeared had  combined  with  the  ice,  and  its  effect 
had  been,  not  to  raise  its  sensible  temperature,  but 
simply  to  convert  the  solid  body  into  a liquid  one, 
so  that  the  caloric  had  become  latent , or  impercepti- 
ble to  the  senses,  as  well  as  incapable  of  being  de- 
tected by  the  most  delicate  thermometer. 

“ So,  then,”  cried  the  boy,  as  the  new  thought 
flashed  upon  him,  u a liquid  is  merely  a solid , whose 
particles  are  kept  asunder  by  so  much  heat , which  is 
insensible  to  us.  In  this  piece  of  wax  the  particles 
are  held  together  by  a certain  force,  which  is  called 
the  i attraction  of  cohesion,’  so  that  when  I press 
upon  it  I am  incapable  of  separating  one  part  of  it 
from  another.  If,  however,  I apply  but  a little  heat 
to  the  substance,  the  cohesion  is  soon  destroyed,  and 
the  particles,  instead  of  then  firmly  adhering  one  to 
another,  become  free  to  move,  and  are,  consequently, 
easily  separable ; so  that  a rod  can  be  plunged  into 
it  when  liquefied,  and  moved  about  in  it  with  little 
or  no  difficulty.” 


THE  "WONDERFUL  EFFECTS  OF  HEAT. 


213 


u Yes,”  lie  repeated,  “ a liquid  is  merely  a solid, 
whose  particles  are  kept  asunder  by  heat.” 

Humphry  was  so  pleased  with  the  result  he  had 
arrived  at,  that  he  varied  the  experiment  in  a num- 
ber of  different  forms. 

First,  he  took  some  spermaceti  (a  substance  which 
melts  at  112°),  and  found  that  a thermometer 
plunged  in  this  (as  in  the  ice)  remained  stationary 
at  the  melting-point  until  the  whole  was  liquefied, 
and  that  it  was  not  till  then  that  the  temperature 
could  be  raised  above  the  point  of  liquefaction. 

Next  he  tried  the  same  experiment  with  some 
lead,  and  found  that,  though  he  heated  a ladle-full 
nearly  red  hot,  the  temperature  of  the  whole  was 
immediately  cooled  down  again  to  the  fusing-point 
by  the  addition  of  a piece  of  the  solid  metal. 

Hence  the  law  was  manifest,  that  in  all  cases  of 
liquefaction  a certain  quantity  of  heat , not  indicated  by 
the  thermometer , is  absorbed , or  disappears — this  heat  be- 
ing withdrawn  from  surrounding  bodies , and  so  leaving 
them  comparatively  cold. 

Accordingly,  now  that  Humphry  had  ascertained 
that  liquefaction  itself  was  a source  of  cold,  he  pro- 
ceeded to  try  what  degree  of  cold  he  could  produce 
by  causing  certain  substances  to  melt  rapidly. 

For  this  purpose  he  took  some  snow  and  sprin- 
kled a little  salt  over  it,  when  he  observed  that  the 
two  solids  immediately  formed  a liquid  ; and  then, 
plunging  a thermometer  into  the  mixture,  he  beheld 


214 


THE  WONDERS  OF  SCIENCE. 


the  quicksilver  sink  and  sink,  until  it  had  nearly 
reached  zero,  so  that  it  fell  from  32°  to  0°.  Then 
the  boy  made  a mixture  of  5 parts  of  smelling  salts, 
5 parts  saltpetre,  and  16  parts  water,  and  plunging 
the  thermometer  into  this,  he  found  that  it  sank 
from  50°  (the  temperature  of  the  room  in  which  the 
experiment  was  made)  to  10°  (which  is  several  de- 
grees below  freezing-point).  With  a mixture,  con- 
sisting of  equal  parts  of  saltpetre,  ammonia,  and 
water,  the  thermometer  fell  6°  lower  than  in  the  pre- 
vious experiment — or  from  50°  to  4°.  Again,  with 
5 parts  of  Glauber’s  salts  and  4 parts  of  oil  of  vitriol 
and  water,  the  temperature  sank  1°  lower  still — or 
from  50°  to  3°.  Further,  having  finely  powdered 
some  of  the  crystals  of  the  last-mentioned  salt,  he 
drenched  them  with  muriatic  acid,  when  the  salt 
dissolved  to  a greater  extent  than  it  had  previously 
done  in  the  water,  and  the  consequence  was  that 
the  temperature  fell  even  lower  than  before — or 
from  50°  to  0°,  while  the  vessel  in  which  the  mix- 
ture was  made  became  covered  with  hoar  frost ; 
and  when  some  water  in  a tube  was  plunged  into 
the  liquefied  salt,  it  was  speedily  converted  into  a 
mass  of  ice. 

Humphry  was  now  anxious  to  see  whether  the 
heat  which  is  absorbed,  and  becomes  latent  or  in- 
sensible during  the  liquefaction  of  bodies,  really  re- 
mains in  the  liquid,  and  whether  it  is  given  out  again 
or  emitted  during  their  solidification. 


THE  WONDERFUL  EFFECTS  OF  HEAT.  215 

To  satisfy  himself  upon  this  point  he  prepared 
two  vessels,  one  full  of  water  and  the  other  full  of 
brine,  the  temperatures  of  the  liquids  in  each  being, 
at  first,  precisely  52°.  On  a very  cold  day,  when 
the  thermometer  stood  at  22°  (i.  e.  10°  below  freez- 
ing-point), the  boy  exposed  the  fluids  in  these  two 
vessels,  with  thermometers  in  each,  to  the  open  air, 
and  found  that  they  both  gradually  parted  with 
their  heat  to  the  surrounding  atmosphere,  and  were 
soon  cooled  down  to  32°  ; then  the  water  began  to 
freeze  very  slowly,  and  during  this  the  thermometer 
in  the  water- vessel  remained  perfectly  stationary. 
The  brine,  however  (which  does  not  congeal  till  its 
temperature  sinks  to  4°),  continued  to  cool  on,  the 
thermometer  in  it  sinking  without  interruption,  un- 
til it  gradually  reached  the  temperature  of  the  ex- 
ternal air,  or  22°. 

Now  it  was  plain  that  both  liquids,  in  cooling, 
were  alike  parting  with  their  heat  to  the  colder  air. 
Why,  then,  should  one  and  not  the  other  suddenly 
cease  giving  out  caloric , and  refuse  for  a certain  time 
to  be  cooled  down  to  the  same  level  as  the  atmos- 
phere around  it? 

The  only  explanation  of  the  problem  was,  that 
the  water,  during  the  process  of  freezing,  was  part- 
ing with  the  140°  of  heat  which  Humphry  had 
before  seen  were  necessary  to  retain  it  in  a liquid 
form,  and  that  it  was  the  evolution  of  this  amount 
of  caloric  which  served  to  keep  the  temperature  of 


216 


THE  WONDERS  OF  SCIENCE. 


the  water  for  a considerable  time  at  32° — notwith- 
standing the  cooling  effect  of  the  surrounding  atrnos- 
nhere. 

-L 

Still  this  experiment  hardly  satisfied  the  boy. 
He  wanted  to  have  some  sensible  proof  of  the  evo- 
lution of  heat  from  water  during  the  act  of  freezing. 
It  was  true,  there  was  no  way  of  accounting  for  the 
fact  of  the  thermometer  remaining  stationary  in  one 
vessel  while  it  was  continually  sinking  in  the  other, 
except  by  supposing  that  the  latent  insensible  heat 
was  being  given  off  from  the  water  as  it  passed  into 
the  solid  form.  Humphry  desired,  howrever,  to  see , 
as  it  were,  the  heat  so  given  off — that  is  to  say,  he 
wished  to  behold  the  thermometer  rise  instead  of 
merely  remaining  fixed  at  one  point. 

Accordingly  it  struck  the  lad,  that  if  he  was  to 
keep  some  water  in  a vessel  perfectly  still,  and  to 
prevent  even  the  air  from  agitating  its  surface,  he 
might  be  able  to  cool  it  down  some  few  degrees 
below  the  freezing-point,  and  then  he  should  be 
able  to  see  if,  in  the  act  of  freezing  afterwards,  the 
thermometer  would  really  rise  as  the  water  solidi- 
fied. So  successfully  did  Humphry  perform  this 
experiment,  that  he  was  enabled,  by  great  care,  to 
cool  some  water  in  a vessel  down  to  22°  without 
freezing  it.  Then  he  felt  a thrill  dart  through  his 
frame  as  he  agitated  the  water,  and  beheld  it  im- 
mediately shoot  into  a thousand  transparent  crys- 
tals— whereupon  the  thermometer  in  the  vessel  in- 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


217 


stantly  began  to  rise,  and  soon  stood  at  32°,  thus 
showing  that  the  water  had  acquired  10°  of  heat 
almost  in  an  instant. 

Whence  came  this  heat,  then? 

But  one  answer  was  possible.  It  was  manifest 
that  the  water,  in  the  act  of  solidifying,  gave  out 
heat,  even  as  in  the  act  of  liquefying  ice  absorbed 
it. 

“ But  do  all  things,”  said  Humphry  to  himself, 
u give  off  heat  as  they  pass  from  a liquid  to  a solid 
form?  And  is  solidification,  therefore,  a heating 
process  to  surrounding  bodies,  in  the  same  manner 
as  liquefaction  (from  the  absorption  of  heat  at  such 
times)  is  a cooling  one?” 

The  youth  had  heard  that,  if  a strong  solution  of 
Glauber’s  salts  be  poured,  while  hot,  into  a flask, 
and  corked  tightly  down,  it  will  remain  liquid  when 
cold,  and  that  on  removing  the  cork  it  will  imme- 
diately shoot  into  a fibrous  mass  of  crystals.  He 
wished  to  see,  therefore,  whether,  in  the  act  of  solid- 
ification, heat  is  evolved  from  such  a solution. 

Humphry  was  not  long  in  preparing  the  requi- 
sites for  the  experiment,  and  was  then  delighted  to 
find,  as  he  watched  the  crystals,  immediately  that 
he  withdrew  the  cork,  dart  from  the  surface  down- 
wards, the  temperature  of  the  substance  became  so 
much  increased,  that  the  bottle  which  contained  it 
grew  sensibly  warm  in  his  hand,  though  it  was  per- 
fectly cold  before. 


218 


THE  WONDERS  OF  SCIENCE. 


Now  the  lad  knew,  that  in  making  the  solution 
he  had  added  2 ounces  of  water  to  3 ounces  of  the 
salts,  and  as  the  whole  of  this  became  solidified  on 
opening  the  bottle,  it  was  clear  that  the  elevation  of 
temperature  arose  principally  from  the  solidification 
of  the  ivater  in  the  crystalline  mass. 

Next  Humphry  added  a saturated  solution  of 
tartaric  acid  to  some  strong  liquid  ammonia,  and 
found,  immediately  that  the  two  fluids  were  poured 
together,  a solid  substance  was  thrown  down,  and 
considerable  heat  evolved. 

Again,  the  lad  was  aware  that,  on  mixing  pow- 
dered plaster  of  Paris  with  water,  there  is  a like 
increase  of  temperature  at  the  moment  of  the  com- 
position u setting or,  in  other  words,  when  the  wa- 
ter with  which  the  plaster  has  been  mixed  passes 
into  the  solid  form. 

Further,  he  could  now  perceive  that  the  great  in- 
crease of  heat  which  occurs  during  the  slacking  of 
lime  is  due  merely  to  the  same  cause,  viz.  the  solidi- 
fication of  the  ivater  poured  upon  it.  Consequently 
it  was  plain  that  water,  in  passing  from  the  liquid 
to  the  solid  form,  invariably  evolves  the  heat  which 
is  necessary  to  retain  it  in  a liquid  state,  and  which 
as  it  passes,  on  the  other  hand,  from  the  solid  to  the 
liquid  state,  it  as  invariably  absorbs. 

Not  only,  however,  is  there  an  increase  of  tem- 
perature when  water  becomes  solid,  but  Humphry 
found  the  same  result  to  ensue,  even  when  the  same 


THE  WONDERFUL  EFFECTS  OF  HEAT.  219 

liquid  is  condensed.  On  mixing  4 parts  of  strong 
oil  of  vitriol  with  1 part  of  water,  cooled  down  to 
the  freezing-point,  he  perceived  that  the  two  to- 
gether occupied  considerably  less  space  than  they 
did  alone,  and  that  the  mixture  rose  rapidly  from 
32°  to  212°,  or  from  the  freezing  to  the  boiling  point. 
The  same  result  ensued  when  1 part  of  snow  was 
substituted  for  the  1 part  cold  water ; but,  strange 
to  say,  when  the  proportions  were  reversed,  so  that 
there  were  4 parts  of  snow  to  1 part  of  oil  of  vitriol, 
intense  cold  instead  of  intense  heat  wak  produced — 
the  increase  of  temperature  in  the  one  case  arising 
from  the  condensation  of  the  water  from  the  snow, 
and  the  decrease  of  temperature,  on  the  other  hand, 
being  due  to  the  liquefaction  of  the  snow  itself. 

Moreover,  the  boy  was  aware  that  a piece  of  soft 
iron,  when  hammered,  becomes  intensely  heated ; and 
he  had  heard  that  when  a bar  of  red-hot  iron  is  pass- 
ed through  a rolling-mill,  its  temperature  is  so  much 
raised  that  it  is  rendered  nearly  white-hot  by  the 
extreme  pressure,  and  the  consequent  condensation 
of  the  particles. 

Sudden  expansion , on  the  other  hand,  Humphry 
found  to  be  a cooling  process ; and  this  is  one  of 
the  reasons  why  high-pressure  steam,  on  issuing  from 
a small  apertur©,  instead  of  scalding  the  hand  as  or- 
dinary steam  would,  scarcely  feels  warm,  even  though 
its  temperature  be  some  hundred  degrees  higher  than 
the  vapour  at  a low  pressure ; for  as  the  compressed 


220 


THE  WONDERS  OE  SCIENCE. 


steam  escapes  into  the  atmosphere,  its  instantaneous 
expansion  so  far  cools  it,  that  it  is  deprived  of  all 
power  of  burning. 

Moreover,  at  the  fountain  of  Hicro,  in  Hungary, 
a part  of  the  machinery  for  working  the  mines  con- 
sists of  a column  of  water  260  feet  high,  which 
presses  upon  a large  volume  of  air,  enclosed  in  a 
tight  reservoir,  so  that  the  air  within  is  greatly 
condensed  by  the  enormous  weight  of  the  water; 
and  that  when  a pipe  communicating  with  this  res- 
ervoir is  suddenly  opened,  the  condensed  air  rushes 
out  with  extreme  velocity,  and  then  instantly  ex- 
panding, absorbs  so  much  heat  as  to  precipitate  the 
moisture  it  contains  in  a shower  of  snow  — a hat 
held  in  the  blast  being  immediately  covered  with  it. 
So  strong,  however,  is  the  current  of  condensed  air, 
that  the  workman  who  holds  the  hat  is  obliged  to 
lean,  his  back  against  the  wall  to  retain  it  in  its  po- 
sition. 

Another  illustration  of  the  cooling  effect  produced 
by  the  sudden  expansion  of  condensed  air  is  afforded 
in  the  fact,  that  if  the  blast  from  an  air-gun  be  di- 
rected upon  a delicate  thermometer,  the  temperature 
will  be  found  to  be  lowered  at  the  moment  of  the 
discharge. 

As  yet  Humphry  had  dealt  only  with  the  effects 
produced  by  the  conversion  of  solids  into  liquids, 
or  liquids  into  solids,  and  there  still  remained  for 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


221 


him  to  learn  what  results  ensued  when  liquids  were 
changed  into  vapours , or  vapours  into  liquids. 

Accordingly  he  proceeded  to  heat  some  water  in 
an  open  vessel,  and  found,  as  the  temperature  grad- 
ually rose,  that  the  vapour  continued  to  form  on  its 
surface  till  the  thermometer  reached  212°,  when 
the  liquid  became  violently  agitated.  But  then, 
although  the  fire  was  kept  up  beneath  the  vessel 
as  strong  as  at  first,  and  the  heat  continued  to  flow 
into  it  as  before , the  quicksilver  in  the  thermome- 
ter became  stationary,  and  remained  so  until  the 
whole  of  the  liquid  had  been  dissipated  in  the  form 
of  steam. 

Here,  then,  was  another  instance  of  the  absorp- 
tion of  heat  during  a change  of  form  ; and  it  was 
evident,  that  as  water  required  a certain  amount 
of  temperature  in  order  to  convert  it  from  a solid 
into  a liquid  state,  so  did  it  need  a proportionate 
supply  of  heat  to  change  it  from  a liquid  into  a 
vapour. 

u The  heat  absorbed  during  the  boiling  passed  off, 
perhaps,  in  the  steam,”  thought  Humphry. 

On  testing  the  temperature  of  the  vapour,  how- 
ever, it  was  found  to  be  no  hotter  than  that  of  the 
water  during  its  ebullition. 

What,  then,  had  become  of  the  heat  which  had 
been  added  since  the  boiling  commenced'? 

W'hy,  it  had  been  rendered  latent  or  insensible , 
being  necessary  for  retaining  the  liquid  in  a more 


222 


THE  WONDERS  OF  SCIENCE. 


rarified  form ; for  as  a liquid  is  but  a solid  whose 
particles  have  been  separated,  and  so  made  free  to 
move,  by  the  latent  heat  existing  between  them,  so 
a vapour  is  merely  a liquid,  whose  atoms  have  been 
driven  farther  asunder,  and  made  still  more  easily 
separable,  by  the  heat  imbibed  during  the  process 
of  vaporization.  It  was  evident,  therefore,  that  the 
production  of  vapour  is  attended  with  a loss  of  sens- 
ible heat,  and  that,  as  in  the  case  of  liquefaction, 
heat  disappears  in  order  to  constitute  the  liquid,  so 
in  the  case  of  evaporation  a considerable  quantity 
of  heat  becomes  latent  in  the  vapour. 

To  render  this  part  of  the  subject  still  more 
clear,  Humphry  filled  a flat-bottomed  tin  vessel 
with  a definite  quantity  of  water,  at  the  tempera- 
ture of  50°.  Then,  having  placed  the  vessel  upon 
a heated  plate,  he  found  that  in  4 minutes  it  had 
acquired  a temperature  of  212°,  and  began  to  boil, 
whilst  in  20  minutes  the  whole  had  evaporated, 
having  been  dissipated  in  the  form  of  steam.  The 
water,  therefore,  hadreceived  212° — 50°,  or  162°  of 
heat  in  4 minutes,  which  is  at  the  rate  of  40^°  in 
each  minute.  The  heat,  however,  continued  to  flow 
into  the  water  at  the  same  rate  during  the  whole  20 
minutes,  so  that  the  entire  amount  of  heat  received 
must  have  been  40^°  x 20,  or  810°,  and  this  had 
become  latent  in  the  steam.  Consequently  the  total 
quantity  of  heat  required  to  evaporate  boiling  water 
would  be  sufficient  to  raise  the  water— provided  it 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


223 


remained  all  the  time  in  the  liquid  state,  instead  of 
being  converted  into  steam — as  much  as  810°  above 
the  boiling-point,  or  altogether  to  1022°. 

To  verify  this  conclusion,  Humphry  heated  some 
water  under  pressure  in  a “Papin’s  digester,”  so  that 
the  liquid  was  prevented  evaporating,  and  raised  the 
temperature  of  it  to  400°.  Then  the  lad  opened 
the  valve,  and  part  of  the  water  suddenly  rushed 
out  in  the  form  of  steam,  when  the  temperature 
of  that  remaining  in  the  digester  sank  immediate- 
ly to  212°.  Consequently  188°  (400°  — 212°)  of 
heat  had  suddenly  disappeared,  having  been  car- 
ried off  by  the  steam.  It  was  afterwards  found  that 
only  ith  of  the  water  had  gone  off  in  vapour,  so  that 
this  vapour  must  have  contained  not  only  its  own 
188°,  but  the  188°  lost  by  the  4 other  parts  re- 
maining in  the  digester;  that  is  to  say,  the  steam 
must  have  contained  188°  x 5,  or  940°  of  heat  al- 
together. This  experiment  therefore  showed,  that 
steam  is  water  combined  with  nearly  1000°  of  heat ; 
and  in  the  same  manner  as  the  water  had  been  pre- 
viously observed  to  give  out  its  heat  of  liquidity,  and 
to  make  the  thermometer  rise  at  the  moment  of 
its  conversion  into  ice,  so  was  it  now  seen  to  absorb 
a considerable  amount  of  heat,  and  to  make  the 
thermometer  fall  at  the  moment  of  its  conversion 
into  vapour. 

Evaporation,  therefore,  should  be  a means  of  pro- 
ducing cold,  in  the  same  manner  as  liquefaction  had 


224 


THE  WONDERS  OF  SCIENCE. 


been  previously  proved  to  be ; for  if  it  be  necessary, 
in  order  to  convert  liquids  into  vapours,  that  a cer- 
tain amount  of  heat  be  absorbed,  it  is  plain  that 
such  heat  must  be  drawn  from  surrounding  substan- 
ces,  and  thus  the  vaporization  of  one  body  will  be 
a cooling  process  to  others  near  it. 

To  test  this,  Humphry  spread  out  a wet  cloth  in 
a keen  wind  when  the  atmosphere  was  a few  de- 
grees above  the  freezing-point,  and  found  that  the 
particles  of  water,  as  they  passed  into  the  form  of 
vapour,*  carried  oft*  so  much  heat  from  the  liquid 
in  the  cloth  (in  the  same  manner  as  the  steam  did 
in  the  Papin’s  digester)  that  the  remainder  became 
frozen,  while  the  cloth  itself  was  rendered  hard  and 
stiff  by  the  formation  of  ice  in  its  pores. 

Humphry,  however,  knew  that  ether  was  much 
more  vaporisable  than  water  at  ordinary  tempera- 
tures. Accordingly  he  availed  himself  of  this  sub- 
stance in  the  production  of  cold  by  spontaneous 
evaporation. 

First,  he  folded  a strip  of  cambric  round  the 
bulb  of  a small  thermometer,  and  allowed  some 
ether  to  dribble  over  it,  while  he  increased  the 
evaporation  by  projecting  a current  of  air  upon  it 
by  means  of  a bellows.  The  quicksilver  was  im- 
mediately seen  to  fall  several  degrees  below  the 
freezing-point,  and  on  substituting  a thin  glass  tube 

* Evaporation  goes  on  more  or  less  rapidly  at  all  tempera- 
tures. 


THE  WONDERFUL  EFFECTS  OF  HEAT.  225 

containing  a small  quantity  of  water  for  the  ther- 
mometer previously  used,  the  boy  was  enabled  to 
produce  ice  by  the  same  means. 

Next,  the  lad  made  use  of  the  air-pump  which  he 
had  previously  constructed  out  of  the  rudest  mate- 
rials,* in  order  to  facilitate  the  spontaneous  evapo- 
ration of  water,  by  removing  the  pressure  of  the  at- 
mosphere from  the  surface  of  it. 

Upon  the  plate  of  the  apparatus  he  placed  a soup- 
plate,  and  this  he  half  filled  with  oil  of  vitriol ; above 
the  soup-plate  he  stood  a tin  basin,  supported  on 
three  pieces  of  tobacco-pipe,  and  three  parts  filled 


* Dr.  Paris,  in  his  “ Life  of  Davy”  (p.  37),  relates  the  follow- 
ing anecdote  concerning  the  construction  of  this  apparatus  : “ A 
French  vessel  having  been  wrecked  off  the  Land’s  End,  the  sur- 
geon escaped,  and  found  his  way  to  Penzance.  Accident  brought 
him  acquainted  with  Humphry  Davy,  who  showed  him  many 
civilities,  and  in  return  received,  as  a present  from  the  surgeon, 
a case  of  instruments  which  had  been  saved  from  the  ship.  The 
contents  were  eagerly  turned  out  and  examined  by  the  young 
chemist ; not,  however,  with  any  professional  view  as  to  their 
utility,  but  in  order  to  ascertain  how  far  they  might  be  con- 
vertible to  experimental  purposes.  The  old-fashioned  and  clum- 
sy glyster  apparatus  was  viewed  with  exultation,  and  seized  in 
triumph.  What  reverses  may  not  be  suddenly  effected  by  a 
simple  accident ! So  says  the  moralist.  Reader,  behold  an  il- 
lustration : in  the  brief  space  of  an  hour  did  this  long-neglected 
and  unobtrusive  machine,  emerging  from  its  obscurity  and  insig- 
nificance, figure  away  in  all  the  pomp  of  a complicated  piece  of 
pneumatic  apparatus.  Nor  did  its  fortunes  end  here ; it  was 
destined  for  greater  things  ; and  we  shall  hereafter  learn  that  it 
actually  performed  the  duties  of  an  air-pump  in  an  original  ex- 
periment on  the  nature  and  sources  of  heat.”  It  is  but  right  to 
add,  that  Dr.  Davy  doubts  the  truth  of  the  above  story. 

P 


226 


THE  WONDERS  OF  SCIENCE. 


with  water,  in  which  a small  thermometer  was  im- 
mersed ; while  over  the  whole  he  put  the  glass  re- 
ceiver. The  arrangement  is  shown  in  the  annexed 
illustration : 


The  pump  was  now  set  to  work,  and  the  air 
gradually  drawn  out  from  the  glass  receiver,  where- 
upon the  thermometer  was  observed  to  sink ; for  as 
the  pressure  of  the  atmosphere  was  removed  the 
evaporation  from  the  water  was  increased,  while 
the  oil  of  vitriol  at  the  bottom  served  to  absorb  the 
vapour  as  fast  as  it  was  produced : so  that,  though 
the  temperature  was  considerably  lowered,  the  evap- 
oration from  the  water  ultimately  became  so  rapid 
that  it  had  all  the  appearance  of  boiling,  and  in  the 
course  of  5 or  10  minutes  the  liquid  was  converted 
into  ice. 

Before  the  solidification  took  place,  however,  the 
thermometer  was  observed  to  fall  several  degrees 
below  the  freezing-point,  whilst  at  the  moment  of 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


227 


its  freezing  it  rose  to  32°,  in  consequence  of  the 
escape  of  the  heat  which  had  previously  served  to 
keep  the  water  liquid. 

The  explanation  of  the  process  is  almost  obvious. 
As  in  the  case  of  the  steam  issuing  from  the  Papin’s 
digester,  that  part  of  the  water  passing  off  in  the 
form  of  vapour  abstracted  heat  from  the  remainder 
of  the  fluid  portion,  which,  thus  losing  the  caloric 
that  served  to  keep  it  liquid,  became  solid,  or  froze. 

Humphry  was  now  anxious  to  see  what  effect  the 
simultaneous  evaporation  of  ether  and  water  would 
produce  under  the  air-pump.  Accordingly  he  pro- 
cured a thin  glass  flask,  and  this  he  inserted  in  a 
tumbler,  so  that  it  fitted  almost  close.  Having 
poured  a little  ether  into  the  flask,  and  some  cold 
water  into  the  tumbler,  he  placed  the  whole  appa- 
ratus under  the  receiver  of  the  air-pump,  as  here 
represented : 


On  exhausting  the  receiver  the  ether  was  ob- 


228 


THE  WONDERS  OP  SCIENCE. 


served  to  boil , from  the  rapidity  of  its  evaporation, 
while  the  water  in  which  it  was  immersed  soon  be- 
came solidified,  or  converted  into  ice. 

The  apparent  anomaly  of  two  liquids  made  to 
boil  and  freeze  at  one  and  the  same  time  puzzled 
the  lad  for  a while.  At  length,  however,  he  divined 
the  reason.  The  ether,  in  passing  into  the  form  of 
vapour,  required  a certain  amount  of  heat  to  sus- 
tain it  in  that  state,  and  this  it  absorbed  principal- 
ly from  the  water  that  surrounded  it,  which  soon 
became  congealed  owing  to  the  loss  of  that  portion 
of  heat  which  was  requisite  for  its  maintenance  in 
a fluid  form. 

Humphry  had  now  discovered  that,  by  removing 
the  pressure  of  the  atmosphere,  the  evaporation  of 
liquids  proceeded  at  a much  greater  rate,  and  he 
was  anxious  to  learn  whether  they  could  be  made 
to  boil  at  a lower  temperature  by  the  same  means. 

Accordingly,  he  fitted  a stop-cock  into  the  neck 
of  a Florence  flask,  and  then  turning  the  cock  on, 
so  that  the  vapour  might  escape,  he  proceeded  to 
heat  the  water,  over  the  flame  of  a spirit-lamp,  till  it 
boiled;  whereupon  he  removed  the  flask  from  the 
flame  and  closed  the  cock.  The  liquid  then  soon 
ceased  to  boil ; on  plunging  the  flask,  however,  into 
a vessel  of  cold  water,  he  found  the  ebullition  in- 
stantly to  recommence,  but  to  cease  again  directly 
the  vessel  was  held  near  the  fire  or  over  the  lamp. 
Now  during  the  boiling,  in  the  first  instance,  all 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


229 


the  air  above  the  liquid  had  been  driven  out  of  the 
flask,  and  replaced  by  an  atmosphere  of  steam  ; this, 
upon  plunging  the  vessel  into  cold  water,  had  be- 
come condensed  into  a liquid  form,  so  that  a vacu- 
um being  formed  above  the  water,  the  fluid  boiled 
at  a lower  temperature  under  the  diminished  press- 
ure. On  removing  the  flask,  however,  from  the  cold 
medium,  a new  atmosphere  of  steam  was  generated, 
and  the  pressure  of  this  on  the  surface  of  the  liq- 
uid prevented  its  boiling  any  longer ; and  thus  the 
water  was  made  to  boil  by  being  cooled , and  to  cease 
boiling  by  being  heated. 

Humphry  afterwards  ascertained,  that  if  a glass 
of  water  of  the  temperature  of  90°  or  100°  be  placed 
under  the  receiver  of  an  air-pump,  and  the  pressure 
of  the  atmosphere  removed  by  exhausting  the  air, 
the  water  boils  violently  at  that  temperature,  and 
continues  to  do  so  until  the  whole  receiver  becomes 
filled  with  the  vapour;  which  then,  pressing  upon 
the  surface  of  the  liquid,  again  prevents  its  ebullition. 
By  continuing  to  pump  out  the  vapour,  however, 
the  boy  was  enabled  to  keep  the  water  boiling  at  no 
less  than  112°  below  its  boiling-point  in  the  open 
air. 

With  alcohol  and  ether,  however,  it  was  not  even 
necessary  to  warm  them,  for  these  fluids  boil  under 
the  air-pump  at  all  ordinary  temperatures. 

It  has  likewise  been  found  that  water  boils  at 


2S0 


THE  WONDERS  OF  SCIENCE. 


less  than  212°  upon  the  summits  of  hills  and  mount- 
ains, where  the  pressure  of  the  atmosphere  is  con- 
siderably diminished.  At  the  top  of  Mont  Blanc 
water  has  been  made  to  boil  at  187°,  and  even  when 
the  air  is  lighter  at  the  surface  of  the  earth  the 
boiling-point  of  all  liquids  is  reduced ; so  that  in 
this  country,  where  the  density  of  the  atmosphere 
fluctuates  considerably,  water  boils  sometimes  at  2° 
lower  than  212°,  whilst  on  heavy  days  it  requires 
to  be  raised  to  214°  in  order  to  produce  ebulli- 
tion. Even  the  cleanliness  of  the  vessels  in  which 
the  liquid  is  heated  has  been  ascertained  to  alter 
the  boiling-point.  In  glass  vessels,  from  which  all 
chemical  and  mechanical  impurities  have  been  re- 
moved by  perfect  cleaning,  water  may  have  its 
temperature  raised  as  high  as  220°  without  being 
made  to  boil ; whereas  a few  metallic  filings,  or 
other  finely-divided  or  insoluble  materials,  have  the 
effect  of  causing  it  to  boil  at  a lower  temperature 
than  212°. 

Humphry  would  now  have  sought  to  learn  how 
much  water  becomes  expanded  in  passing  into  the 
form  of  steam.  But,  though  he  made  several  rude 
experiments  on  the  subject,  he  was  unable,  from  the 
want  of  proper  apparatus,  to  arrive  at  any  definite 
result,  and  so  was  obliged  to  rest  contented  with 
the  knowledge  which  his  books  afforded  him ; viz. 
that  a cubic  inch  of  water  becomes  converted,  at 


THE  WONDERFUL  EFFECTS  OF  HEAT  231 

212°,  into  very  nearly  a cubic  foot  of  steam,  the 
expansion  being  about  1700  times  the  bulk  of  the 
original  fluid. 

Spirits  of  wine,  on  the  other  hand,  expand  only 
493  times,  ether  about  212  times,  and  oil  of  tur- 
pentine 192  times;  each  at  the  temperature  of  212°. 
Steam,  however,  is  lighter  than  air — whereas  the 
vapours  of  spirits  of  wine,  ether,  and  turpentine, 
are  much,  heavier  than  it,  the  last  being  nearly  5 
times  the  density  of  our  atmosphere  at  the  same 
temperature. 

Before  quitting  this  part  of  the  subject,  there  is 
one  striking  anomaly  connected  with  the  production 
of  vapour  that  deserves  mention  here,  though  it  is 
but  a recent  discovery. 

If  a silver,  or  other  metal  spoon,  be  heated  to  red- 
ness in  the  flame  of  a lamp,  and  some  water  be 
dropped  into  it  while  red  hot,  it  will  be  found  that 
the  liquid,  instead  of  passing  otf  at  once  into  steam, 
will  instantly  assume  a globular,  or  spheroidal  form, 
and  float  about  the  heated  metal,  revolving  with  ra- 
pidity, and  evaporating  very  slowly ; while  the  tem- 
perature of  the  liquid  will  remain  constantly  below  the 
boiling  point — so  long  as  the  red  heat  is  maintained. 
If,  however,  the  lamp  be  withdrawn,  the  water,  as 
the  spoon  cools  down,  will  suddenly  be  made  to  boil 
with  violence,  and  be  dissipated  in  vapour  with  al- 
most explosive  energy. 

The  cause  of  this  singular  phenomenon  is,  that 


232 


THE  WONDERS  OF  SCIENCE. 


the  water  is  separated  from  the  red-hot  metal  by  an 
atmosphere  of  highly-elastic  steam,  which  is  genera- 
ted immediately  the  liquid  is  projected  on  the  heat- 
ed surface,  and  which,  encircling  the  water,  serves  to 
keep  it  in  a spheroidal,  or  globular  state  ; whilst  the 
vapour,  being  a bad  conductor  of  heat,  prevents  the 
temperature  of  the  hot  metal  being  communicated  to 
the  fluid  in  connexion  with  it. 

This  is  the  reason  why  water,  when  accidentally 
dropped  upon  the  heated  bars,  or  hobs  of  a grate, 
is  occasionally  observed  to  run  along  them  like  glob- 
ules of  quicksilver.  If  these,  however,  be  smartly 
struck  with  a hammer,  so  as  to  brins;  them  sudden- 
ly  into  contact  with  the  hot  metal,  the  globules 
will  be  instantaneously  converted  into  steam,  and 
the  change  of  form  attended  with  a slight  explo- 
sion. 

Another  form  of  the  same  singular  phenome- 
non consists  in  plunging  a mass  of  white-hot  metal 
into  a vessel  of  cold  water,  when  the  incandes- 
cence will  be  found  to  continue,  rather  than  to  be 
quenched,  in  the  liquid,  the  metal  still  shining 
with  a bright  white  light,  while  the  water  may  be 
seen  to  circulate  around,  though  at  some  distance 
from,  the  glowing  mass,  being  separated  from  it  by 
an  atmosphere  of  non-conducting  vapour,  which, 
for  a time,  prevents  its  heat  being  communicated 
to,  and  so  reduced  by,  the  surrounding  fluid.  At 
length,  as  the  metal  cools,  the  water  around  it  is 


THE  WONDERFUL  EFFECTS  OF  HEAT.  233 

brought  into  contact  with  the  heated  surface,  when 
it  is  made  suddenly  to  boil  with  energy. 

Moreover,  if  an  iron  shell  containing  water  be 
made  red  hot,  and  a hole  then  drilled  in  it,  no  water 
will  be  found  to  flow  through  the  orifice  until  the 
iron  has  been  considerably  cooled,  when  it  will  sud- 
denly issue  forth  with  great  violence,  in  the  form  of 
steam. 

So,  again,  if  water  be  poured  upon  an  iron  sieve, 
the  wires  of  which  have  been  heated  to  redness,  it 
will  not  pass  through  the  interstices.  As  the  sieve 
cools  down,  however,  it  will  be  found  to  run  through 
rapidly. 

Further,  if  a red-hot  cinder  be  let  fall  into  a pan 
of  water,  it  will  be  seen  to  swim  upon  the  surface, 
and  then  to  sink  with  a hissing  sound,  accompanied 
with  a sudden  irruption  of  steam. 

But  a far  more  striking  illustration  of  this  strange 
property  consists  in  heating  to  redness  a silver  or 
platinum  capsule  (or  small  crucible),  and  filling  it 
while  red  hot  with  a freezing  mixture,  when  the 
whole  mass  will  instantly  be  thrown  into  the 
spheroidal  state,  and  on  introducing  a thermometer 
therein  the  temperature  of  the  liquid  will  be  found 
to  be  scarcely  increased,  so  that  a small  tube  filled 
with  water  soon  becomes  frozen  when  immersed  in 
it ; and  thus  ice  may  thus  he  produced  even  in  a ves- 
sel, the  heat  of  which  is  no  less  than  1000°.  Indeed, 
by  introducing  some  ether  and  solid  carbonic  acid 


234 


THE  WONDERS  OF  SCIENCE. 


into  an  incandescent  crucible,  even  quicksilver  itself 
has  been  made  to  freeze  in  it,  though  this  requires 
a temperature  of  82°  below  the  freezing-point  of 
water ; and  yet  this  extreme  cold  (equal  to  that  of 
a Polar  winter)  has  been  produced,  and  mercury  fro- 
zen inside  a red-hot  vessel. 

Humphry,  however,  was  anxious  not  to  conclude 
his  investigations  concerning  the  changes  of  form 
produced  by  heat  without  ascertaining  whether  all 
bodies,  in  passing  from  a lower  to  a higher  tem- 
perature— or,  on  the  other  hand,  from  a higher  to  a 
lower  one — absorbed  the  same  quantities  of  calo- 
ric ; that  is  to  say,  did  one  body  require  a greater 
amount  of  heat  to  raise  it  to  a given  temperature 
than  another,  and  did  some  bodies  give  off  more  heat 
than  others  in  cooling? 

First,  the  lad  dealt  with  equal  quantities  of  the 
same  fluid  at  different  temperatures,  in  order  to  de- 
termine whether,  on  mixing  the  two  together,  the 
resulting  temperature  amounted  to  the  mean  of  both. 
He  added  \ pint  of  cold  water  at  50°  to  -§•  pint  of 
warm  water  at  100°  and  found  that  the  two  to- 


gether gave  a mean  temperature  of  75° 


so  that  the  hot  water  had  lost  25°,  wdiilst  the  cold 
had  gained  precisely  the  same  amount. 

Then  Humphry  proceeded  to  try  whether  the 


result  was  the  same  with  equal  quantities  of  dif- 


THE  WONDERFUL  EFFECTS  OF  HEAT.  235 

ferent  fluids.  Accordingly,  he  took  the  same 
amount  of  water  at  50°  as  he  had  previously  em- 
ployed for  one  portion,  but,  instead  of  the  water 
at  100°  for  the  other,  he  substituted  a like  quantity 
of  quicksilver  at  the  same  temperature,  and  found 
to  his  astonishment,  on  pouring  the  one  to  the 
other,  that  the  heat  of  both  together  was  no  longer 
the  mean  of  the  two  (or  75°  as  before),  but  only 
66f°.  In  this  case,  therefore,  the  quicksilver  had 
lost  as  much  as  33^°  (100  — 66§),  whilst  the  water 
had  gained  only  16f°  (66§ — 50) ; so  that  the  quick- 
silver had  parted  with  tivice  as  much  heat  as  the 
water  had  absorbed.  Consequently  it  was  evident 
that,  in  order  to  raise  a certain  measure  of  water  to 
a given  temperature,  it  required  just  double  the 
quantity  of  heat  to  be  added  to  it  that  an  equal 
measure  of  quicksilver  did ; or,  in  other  words, 
the  capacity  of  water  for  heat  was  twice  that  of 
quicksilver. 

This  referred,  however,  only  to  equal  measures 
of  the  two  fluids  ; so  Humphry  wished  to  ascertain 
whether  the  effect  would  be  the  same  with  equal 
weights  of  them.  He  mixed,  therefore,  1 pound  of 
water  at  50°  with  1 pound  of  quicksilver  at  100°, 
and  discovered  that  the  resulting  temperature  was 
not  quite  52°.  Here,  then,  the  quicksilver  had 
lost  rather  more  than  48°  of  heat,  while  this  amount 
had  served  to  increase  the  warmth  of  the  water 
only  about  2°.  There  was  but  one  conclusion  to 


236 


THE  WONDERS  OP  SCIENCE. 


be  arrived  at,  therefore ; namely,  that  the  capacity 
of  a given  weight  of  water  for  heat  is  about  30 
times  greater  than  an  equal  iveight  of  quicksilver, 
whereas  the  capacity  of  a given  measure  of  the  for- 
mer is  only  twice  that  of  an  equal  measure  of  the 
latter. 

After  this  the  boy  added  1 pound  of  water  at 
50°  to  an  equal  iveight  of  spermaceti  oil  at  100°, 
when  the  temperature  of  the  mixture  was  found  to 
be  66  §°  ; so  that  the  oil  had  parted  with  twice  as 
much  heat  as  the  water  had  gained. 

Thus  it  was  evident  that  different  substances 
required  different  quantities  of  heat  to  raise  them 
to  the  same  temperature ; and  that  in  order  to 
warm  a certain  weight  of  water  to  the  same  degree 
as  an  equal  weight  of  oil  and  quicksilver,  twice 
as  much  heat  must  be  given  to  the  water  as  to 
the  oil,  and  30  times  as  much  as  to  the  quick- 
silver. 

Still  the  cautious  boy  was  anxious  to  test  the 
truth  of  this  result  by  another  experiment. 

Accordingly,  he  took  1 pound  weight  of  each  of 
the  three  substances  above  mentioned,  and  having 
brought  them  severally  to  a temperature  of  50°,  he 
placed  the  flasks  in  which  they  were  respectively 
contained  in  a large  bath  of  warm  water,  the  heat 
of  which  he  kept  constantly  at  100°.  This  done, 
he  proceeded  to  note  the  time  and  manner  in  which 
each  of  the  fluids  was  heated,  and  found  that  when 


THE  WONDERFUL  EFFECTS  OF  HEAT.  237 

the  thermometer  in  the  quicksilver  had  reached 
80°,  that  in  the  oil  stood  at  52°,  while  the  one  in 
the  flask  of  water  marked  only  51°  ; and,  though 
the  three  liquids  ultimately  attained  the  same  tem- 
perature as  the  water-bath  in  which  they  were 
immersed,  the  water  took  30  times  longer  to  acquire 
that  heat  than  the  quicksilver , and  twice  as  long  as  the 
oil. 

Now  it  was  manifest  that  each  of  the  liquids  in 
this  experiment  must  have  been  receiving  heat 
alike,  so  that  the  only  feasible  explanation  was  that 
the  water,  in  order  to  have  its  temperature  raised 
to  a given  degree,  required  30  times  the  quantity 
of  heat  that  the  metallic  fluid  did,  and  double  the 
quantity  of  the  oleaginous  one. 

Nevertheless,  to  avoid  all  possible  chance  of  er- 
ror, Humphry  repeated  the  experiment  in  another 
form,  so  as  to  see  whether,  in  cooling,  the  water 
would  part  with* more  caloric  than  either  the  oil  or 
the  quicksilver ; and  just  as  much  more,  too,  as  it 
had  been  found  to  imbibe  while  being  heated. 

With  this  view  Humphry  filled  three  Florence 
flasks — one  with  a pound  of  water,  another  with  a 
pound  of  oil,  and  the  third  with  an  equal  weight  of 
quicksilver — -all  at  the  temperature  of  212°,  and 
having  placed  each  of  the  flasks  in  a large  funnel, 
that  rested  on  a graduated  glass  jar,  he  surrounded 
them  one  after  another  with  pounded  ice,  as  here 
shown  : 


238 


THE  WONDERS  OF  SCIENCE. 


Water.  Oil.  Quicksilver. 


When  the  fluids  had  been  severally  cooled  down 
to  the  same  temperature  as  the  ice  around  them, 
the  lad  proceeded  to  ascertain,  by  the  quantity  of 
water  produced  by  the  thawing  of  the  ice  surround- 
ing each  flask,  how  much  heat  had  been  given  out  by 
the  three  liquids  respectively,  in  sinking  from  212° 
to  32°  ; and  he  ultimately  found  that  the  hot  wa- 
ter, in  cooling,  had  thawed  twice  as  much  ice  as 
the  hot  oil,  and  30  times  as  much  as  the  equal- 
ly hot  quicksilver.  Hence  it  was  beyond  doubt 
that  water,  at  a given  temperature,  contained  con- 
siderably more  heat  than  either  of  the  other  fluids , 
and  hence  the  reason  why  it  took  a longer  time 
than  they  to  be  warmed  or  cooled  to  the  same 
extent. 


THE  WONDERFUL  EFFECTS  OF  HEAT.  239 

These  experiments  naturally  led  the  boy  to  think 
how  great  a magazine  of  heat  the  sea  must  be,  and 
what  a beneficial  influence  its  slow  rate  of  heating 
and  cooling  must  have  in  equalizing  the  temperature 
of  the  atmosphere.  Quicksilver,  on  the  other  hand, 
however,  having  a small  capacity  for  heat,  and,  con- 
sequently, being  quickly  warmed  and  cooled,  becomes 
of  great  value  as  a liquid  for  the  thermometer,  since 
it  is  this  property  that  gives  great  sensibility  to  the 
instrument. 

It  now  only  remained  for  Humphry  to  ascertain 
the  relative  capacities  for  heat  among  solids.  This 
he  did  by  cooling  down  equal  weights  of  the  metals 
and  other  bodies  under  the  exhausted  receiver  of 
his  air-pump,  and  noting  how  long  they  took  to 
pass  each  from  a like  higher  to  a like  lower  tem- 
perature. 

By  such  means  the  youth  ascertained  that  Lead 
had  the  smallest  capacity  for  heat  among  the 
metals,  cooling  more  rapidly  than  even  quicksilver 
itself,  and  34^  times  quicker  than  water.  Next  in 
order  came  Platinum , which  again  had  less  capacity 
than  quicksilver,  and  cooled  32^  times  quicker  than 
water.  After  this,  Silver  was  found  to  cool  18  times 
quicker  than  water;  Zinc , lOf  times;  Copper , 10^ 
times ; and,  lastly,  Iron , which  was  ascertained  to 
part  with  its  heat  only  9 times  quicker  than  water. 
Glass,  however,  was  found  to  occupy  a longer  time 
in  cooling  than  any  of  the  metals,  giving  off  its  ca~ 


240 


THE  WONDERS  OF  SCIENCE. 


loric  but  8 Jr  times  quicker  than  water ; while  sul- 
phur, on  the  other  hand,  retained  its  warmth  longer 
even  than  glass,  but  still  cooled  5^  times  quicker 
than  water. 

The  capacities  for  heat,  therefore,  among  the 
above-mentioned  substances,  were  inversely  as  their 
rates  of  cooling : that  is  to  say,  lead,  which  cooled 
the  quickest,  contained  the  least  quantity  of  heat, 
and,  therefore,  required  less  caloric  to  raise  it  to  a 
given  temperature ; while  sulphur,  on  the  other  hand, 
which  took  nearly  7 times  as  long  to  cool  as  lead, 
contained  7 times  more  heat,  and  required  to  be 
warmed  for  just  so  much  longer  a period. 

The  relative  capacity  for  heat  among  substances 
is  generally  termed  their  “specific  heat;”  for  as 
different  bodies  are  found  to  possess  unequal  quanti- 
ties of  heat  at  equal  temperatures , and  as  this  exists  in 
them  in  a latent  or  insensible  state,  the  term  specific 
heat  has  therefore  been  adopted  to  express  the  rela- 
tive amount  of  latent  caloric  existing  in  different  sub- 
stances at  the  same  temperatures. 


CHAPTER  X. 


THE  WONDERFUL  EFFECTS  OF  HEAT (concluded). 

m 

The  young  philosopher  had  now  investigated  the 
effects  produced  by  an  elevation  of  temperature,  not 
only  upon  the  bulk,  but  upon  the  form  of  different 
bodies.  He  had  found,  first,  that  heat  increased 
the  size  of  certain  substances,  without  destroying 
the  cohesion  among  their  constituent  particles ; 
and,  secondly,  that  it  loosened  the  attraction  be- 
tween the  atoms  of  other  substances,  and  render- 
ed them  free  to  move : so  that  solids  became  con- 
verted by  it  into  liquids,  and  liquids  into  vapours, 
while  the  heat  which  was  absorbed  and  disappear- 
ed during  the  production  of  such  changes  he  had 
ascertained  not  only  to  exist  between  the  molecules 
of  the  resulting  liquid  or  vapour  in  a latent  or  in- 
sensible state,  but  to  be  again  evolved  in  a sensible 
form  when  the  vapours  became  condensed  or  the 
liquids  solidified. 

The  next  step,  therefore,  was  to  study  the  cir- 
cumstances regulating  the  ignition  and  combustion  of 
bodies. 

Q 


242 


THE  WONDERS  OF  SCIENCE, 


That  there  is  an  intimate  connexion  between  the 
principles  of  light  and  heat,  Humphry  had  little 
doubt.  Indeed,  it  was  plain  to  him  that  the  two 
are  mutually  disposed  to  produce  each  other.  He 
had,  however,  as  yet  considered  only  the  laws  of 
heat,  divested  of  luminosity ; but,  at  present,  he  was 
about  to  examine  the  one  in  connexion  with  the 
other;  the  laws  of  ignition  and  combustion  being 
those  of  the  production  of  artificial  heat,  accompa- 
nied with  light  for  the  time  being. 

Whether  substances,  when  merely  warm , are  ca- 
pable of  emitting  rays  of  light,  it  is  impossible  to 
determine;  “but,”  said  the  lad  to  himself,  “the 
slightest  increase  of  temperature  is  perhaps  accom- 
panied with  some  kind  of  luminous  power  that  our 
sense  of  vision  is  incapable  of  perceiving,  since  it  is 
only  when  the  temperature  of  bodies  is  raised  to  a 
high  point  that  they  acquire  the  property  of  becom- 
ing luminous  to  our  eyes.” 

It  is  extremely  difficult  to  ascertain  the  precise 
temperature  at  which  bodies,  when  heated,  acquire 
the  property  of  giving  out  light ; for  the  result  is 
greatly  modified,  not  only  by  the  sensitiveness  of 
the  eye  of  the  observer,  but  also  by  the  clearness  of 
the  atmosphere  at  the  time  of  making  the  experi- 
ment. 

The  amount  of  heat  necessary  for  producing  lu- 
minosity, however,  certainly  exceeds  650°,  since 
this  is  the  temperature  at  which  quicksilver  boils; 


THE  WONDERFUL  EFFECTS  OF  HEAT.  243 

and  though  Humphry  heated  the  metallic  fluid  to 
ebullition  in  a dark  room,  it  did  not  become,  so  far 
as  he  could  detect,  in  the  least  degree  luminous. 

Subsequent  experiments,  however,  induced  him 
to  place  the  degree  at  which  heated  bodies  begin  to 
emit  light  in  the  dark  at  810°  ; though  the  investi- 
gations which  have  since  been  made  in  connexion 
with  the  subject  lead  to  the  conclusion  that  the  first 
gleam  of  light  which  is  given  out  from  a heated 
platinum  wire  occurs  at  a temperature  of  about 
865°.  The  luminous  rays  emitted  at  this  heat, 
however,  are  not  red,  but  of  a lavender-grey  colour 
(similar  to  those  which  exist  in  the  solar  spectrum 
beyond  the  violet  band),  and  seem  to  be  the  first 
transition  from  darkness  to  ordinary  light. 

At  the  temperature  of  about  1000°  the  light 
emitted  by  the  heated  body  becomes  visible  in  day- 
light, and  is  then  of  a dull-red  hue. 

At  1200°  the  tint  of  incandescence  brightens  into 
a vivid  crimson,  or  “cherry-red,”  as  it  is  termed. 

Then,  as  the  temperature  increases,  the  light  emit- 
ted by  the  glowing  body  assumes  partly  a yellow  col- 
our; so  that  at  1700°  an  “ orange  heat,”  as  it  is 
called,  is  produced. 

At  length,  however,  when  the  heat  rises  to  the 
highest  point,  the  light  emitted  acquires  such  brill- 
iancy as  to  be  painful  to  the  eye ; the  incandescent 
substances  then  appearing  no  longer  tinted,  but 
positively  colourless  in  the  fire.  This  constitutes 


244 


THE  WONDERS  OF  SCIENCE, 


what  is  denominated  a “ white  heat,”  and  occurs  at 
no  less  a temperature  than  3000°.* 

At  this  intense  temperature  a remarkable  change 
is  found  to  occur  in  the  character  of  the  heat  itself, 
for  it  has  been  before  shown  that  the  heat-rays 
emanating  from  an  ordinary  fire  are  stopped  by 
glass ; so  that  while  the  light  emitted  by  the  burn- 
ing coals  passes  freely  through  plates  of  glass,  and  is 
capable  of  being  reflected  by  glass  mirrors,  like  the 
light  of  the  sun  itself,  the  heat  radiated  by  them — 
unlike  that  of  the  solar  beams — has  neither  the  power 
to  traverse  the  transparent  substance,  nor  is  it  sus- 
ceptible of  being  concentrated  into  a focus  by  reflex- 
ion from  a glassy  surface. 

Artificial  heat,  however,  when  at  a very  high  tem- 
perature, is  found  to  have  all  the  properties  of  solar 
heat.  Not  only  does  it  then  admit  of  being  focussed 
by  burning-glasses  in  the  same  manner  as  the  sun- 
beams, but  the  light  emitted  by  it  darkens  solutions 
of  silver  as  effectually  as  the  light  of  day ; so  that 
(as  more  recent  experiments  have  proved)  a photo- 
graphic portrait  can  be  taken  as  well  by  the  rays 
from  coke  at  a white  heat,  as  they  can  by  the  rays 
of  the  sun  itself. 

But  only  those  substances  are  capable  of  being 

* The  highest  temperature  of  a good  blast-furnace  is,  accord- 
ing to  Daniel,  about  equal  to  3300°.  This  constitutes  a “ high 
white  heat  ” 


THE  WONDERFUL  EFFECTS  OF  HEAT.  245 

rendered  incandescent,  which  have  power  to  sus- 
tain the  high  temperatures  requisite  for  ignition, 
without  being  vaporized  or  decomposed  by  the  heat. 
Many  bodies,  however,  are  either  dissipated  or  de- 
stroyed long  before  they  attain  this  intense  temper- 
ature ; while,  on  the  other  hand,  those  termed  com- 
bustibles, when  heated  in  the  air,  burst  into  flame , 
and  undergo  what  is  termed  combustion. 

“ Now  what  is  combustion  V’  said  Humphry  to 
himself,  as  he  thought  over  the  subject.  “ What  are 
the  phenomena  which  occur  when  substances  burn 
with  the  evolution  of  flame?” 

The  boy  knew,  that  formerly  it  was  supposed 
bodies  owed  their  combustibility  to  the  presence  of 
a certain  principle  called  “ phlogiston,”  which  dur- 
ing combustion,  said  the  philosphers,  escaped  from 
them,  producing  light  and  heat ; whereas  when  the 
bodies  had  lost  their  phlogiston — and  had  become 
“ dephlogisticated,”  as  it  was  termed — they  ceased 
to  be  combustible. 

Phlogiston,  however,  Humphry  was  well  aware, 
was  a purely  imaginary  principle,  of  whose  exist- 
ence no  proof  had  been  given,  and  which  had  been 
invented  merely  to  explain  a process  that  appeared 
to  be  otherwise  incomprehensible. 

Moreover,  Humphry  had  learnt  from  the  books 
he  had  already  read  upon  the  subject,  that  the 
metals  were  increased  in  weight  after  being  burnt ; 
so  that  it  was  impossible  to  attribute  the  combus- 


246 


THE  WONDERS  OF  SCIENCE. 


tion  in  such  cases  to  the  escape  of  phlogiston,  since 
it  was  inconceivable  how  a body  could  be  rendered 
heavier  by  losing  something  which  had  previously 
been  combined  with  it. 

Nevertheless,  the  belief  in  this  visionary  phlo- 
giston had  continued  for  nearly  half  a century ; 
and  it  was  only  in  the  year  1775  that  more  correct 
views  had  been  propounded  concerning  the  process. 

At  the  time  of  young  Davy’s  commencing  the 
study  of  this  subject,  Lavoisier’s  new  theory  of 
combustion  had.  been  in  existence  but  a few  years, 
and  the  boy  having  obtained  from  Mr.  Tonkin  the 
loan  of  the  treatise  in  which  the  more  correct  views 
were  originally  propounded,  had  eagerly  perused  the 
volume,  being  not  a little  delighted  with  the  pre- 
cision of  reasoning  and  the  boldness  of  speculation 
contained  in  it. 

Still  Humphry  was  not  satisfied  with  merely 
reading  and  acquiring  the  ideas  of  others.  He  criti- 
cised the  theoretical  speculations  of  the  great  French 
philosopher,  doubted,  and  rejected,  and  advanced 
speculations  of  his  own,  while  speculation  led  him 
to  experiment.* 

* The  above  is  Dr.  Davy’s  account  of  his  brother’s  first  chem- 
ical studies  : “ Such  was  the  commencement  of  Humphry  Da- 
vy’s career  of  original  research,”  he  adds,  “which  in  a few  years, 
by  a succession  of  discoveries,  accomplished  more  in  relation  to 
change  of  theory  and  extension  of  science  than,  in  the  most  ar- 
dent and  ambitious  moments  of  youth,  he  could  either  have  hoped 
to  effect  or  imagined  possible.” 


THE  WONDERFUL  EFFECTS  OF  HEAT.  247 

Humphry  began  the  investigation  of  the  phenom- 
ena of  combustion  by  an  experiment,  to  prove  that 
the  air  in  which  combustibles  are  suffered  to  burn 
till  they  are  extinguished  undergoes  a very  remark- 
able change. 

For  this  purpose  the  lad  put  a little  water  in  a 
soup-plate,  and  on  it  he  placed  a small  piece  of 
candle,  so  that  it  might  swim  on  the  surface. 
Having  lighted  the  wick  he  covered  it  over  with  a 
large  tumbler,  and  found  that  the  candle  then  burnt 
only  for  a short  time,  whilst  immediately  the  flame 
was  extinguished  the  water  rose  in  the  tumbler  con- 
siderably above  its  level  in  the  soup-plate. 

Hence  it  was  evident,  that  the  portion  of  the  air 
which  was  necessary  for  combustion  had  been 
removed  by  the  burning  candle  from  the  atmos- 
phere confined  within  the  tumbler,  and  that,  there- 
fore, it  was  no  longer  capable  of  sustaining  the 
flame. 

“But  maybe,”  thought  Humphry,  “the  candle, 
in  burning,  gives  off  some  gas,  which  is  prejudicial 
to  combustion.” 

So,  to  satisfy  himself  whether  such  were  the 
case  or  not,  the  boy  burnt  some  charcoal  in  an  old 
iron  saucepan,  that  he  had  previously  drilled  full  of 
holes,  in  order  to  admit  the  air.  Then,  having  fit- 
ted a tin  tube  into  the  lid  of  this,  he,  by  means  of 
the  chimney  so  formed,  conducted  the  gas  evolved 
by  the  burning  charcoal  into  a wide-mouthed  bot- 


248 


THE  WONDERS  OF  SCIENCE. 


tie,  that  he  had  previously  filled  and  placed  with  its 
mouth  downwards,  on  a perforated  stand  in  a pail 
of  cold  water ; so  that  as  the  combustion  went  on 
the  gas  produced  kept  bubbling  up  in  the  pail  from 
the  end  of  the  tube,  and  displacing  the  water  as  it 
rose  into  the  inverted  bottle  that  stood  imme- 
diately above  it.  The  arrangement,  however,  will 
be  more  readily  comprehended  by  reference  to  the 
subjoined  engraving : 


As  soon  as  sufficient  gas  had  been  collected 
Humphry  removed  the  tube  from  the  pail,  and 
corked  the  bottle  under  water ; then  having  set 
the  bottle  of  gas  on  a table,  he  attached  a piece  of 
candle  to  the  crooked  end  of  a long  wire,  and 
lowering  this,  while  alight,  into  the  gas,  found,  to 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


249 


his  astonishment,  that  the  flame  was  immediately 
extinguished. 

“So  then,”  cried  the  delighted  boy,  “here  is  a 
kind  of  air  that  I can  neither  see,  nor  feel,  nor 
smell,  and  yet  it  extinguishes  burning  bodies  like 
water.” 

But  Humphry  was  too  eager  to  examine  the 
properties  of  the  gas  he  had  collected  to  wait  to 
reflect  upon  the  curious  results  it  afforded  him. 
Accordingly  he  procured  a tall  glass  jar,  and  hav- 
ing placed  a piece  of  burning  candle  at  the  bottom 
of  this,  he  proceeded  to  empty  the  gas  from  the 
bottle  into  the  jar,  when  to  his  surprise  he  discov- 
ered that  he  could  pour  out  the  heavy  air  that  had 
come  from  the  burning  charcoal  as  though  it  had 
been  a liquid,  while,  immediately  it  fell  upon  the 
lighted  candle  at  the  bottom  of  the  jar,  the  flame 
disappeared  as  suddenly  as  if  so  much  water  had 
been  showered  upon  it. 

After  this  the  boy  amused  himself  by  decanting 
the  gas  backwards  and  forwards  from  one  vessel  to 
the  other,  and  ultimately  found  that  it  was  instan- 
taneously fatal  to  animals,  destroying  sentient  life 
as  rapidly  as  it  extinguished  burning  substances. 

Humphry’s  next  step  was  to  discover  what  sub- 
stance was  capable  of  readily  absorbing  this  gas, 
and  after  many  trials  he  found  that  lime-water  did 
so  with  great  facility. 

Accordingly  he  added  about  an  ounce  of  quick- 


250 


THE  WONDERS  OF  SCIENCE. 


lime  to  a quart  of  water  in  a glass  bottle,  and  cork- 
ing it  up  closely  he  shook  it  several  times,  so  as 
to  dissolve  as  much  of  the  lime  as  possible ; after 
which  he  allowed  it  to  settle,  and  then  decanted  off 
the  transparent  and  colourless  liquid  into  a clean 
bottle  with  a glass  stopper.  This  transparent  solu- 
tion of  lime  in  water  he  then  poured  into  the  glass 
jar  containing  the  gas  from  the  burning  charcoal, 
and  having  corked  the  vessel  tightly  up,  he  shook 
it  about,  and  immediately  perceived  that  the  lime- 
water  was  rendered  turbid  by  the  gas,  being  no 
longer  clear  and  transparent  as  before,  but  changed 
to  an  opaque  milky  white  ; then  having  filtered  the 
turbid  water,  and  so  separated  from  it  all  the  white 
particles  that  had  rendered  the  solution  opaque,  he 
dried  and  weighed  the  sediment,  and  found  that  the 
quantity  of  lime  which  had  been  dissolved  by  the 
water  had  become  nearly  doubled  in  weight  by  the 
gas  which  it  had  absorbed. 

The  youth  had  now  learned  how  to  remove  the 
products  of  combustion,  and  he  was  consequently 
in  a position  to  determine  whether  the  air,  after  a 
substance  had  been  burned  in  it,  really  had  or  had 
not  been  deprived  of  anything  during  the  process. 

Humphry  therefore  placed  a small  quantity  of 
lime-water  at  the  bottom  of  a wide-mouthed  bottle, 
and  through  the  cork  of  this  he  passed  one  end  of  a 
long  wire,  while  to  the  other  end  of  it  he  attached 
a small  piece  of  wax  taper.  This  he  lighted,  and 


THE  WONDERFUL  EFFECTS  OF  HEAT.  251 

then  lowered  down  into  the  air  that  stood  above  the 
lime-water  in  the  vessel.  The  cork  was  now  forced 
tightly  into  the  mouth  of  the  bottle,  and  in  a 
minute  or  two  the  taper  was  extinguished.  After 
this  the  jar  was  shaken  'well  up,  when  the  youth 
beheld,  to  his  great  delight,  the  lime-water  rendered 
turbid  by  the  gas  evolved  during  the  burning  of  the 
taper. 

The  next  step  was  to  discover  whether  the  air 
which  remained  in  the  bottle  (and  from  which  the 
products  of  the  burning  taper  had  been  removed 
by  the  lime-water)  was  still  capable  of  sustaining 
combustion. 

Accordingly  another  lighted  taper  was  lowered 
into  it,  but  this  was  as  rapidly  extinguished  as  the 
one  had  been  by  the  gas  from  the  burning  charcoal 
itself.  It  was  afterwards  found,  too,  that  that  part 
of  the  air  which  remained  after  combustion  was  as 
destructive  of  animal  life  as  even  the  charcoal  gas 
had  been  discovered  to  be. 

“ How  wonderful !”  exclaimed  the  boy,  “ that 
the  atmosphere  round  about  us  should  be  made  up 
of  two  different  kinds  of  air— -one  that  enables 
combustibles  to  burn  and  animals  to  live  in  it,  while 
the  other  immediately  extinguishes  flame  and  de- 
stroys sentient  life ! How  can  I collect  that  portion 
of  the  air  which  supports  combustion  and  maintains 
life,  apart  from  that  which  puts  an  end  to  it  ? I 
should  like  to  see  what  it  would  do  by  itself,  and 


252 


THE  WONDERS  OF  SCIENCE. 


whether  substances  would  bum  brighter  in  it  alone ; 
for  surely  such  must  be  the  case,  since  in  the  at- 
mosphere it  is  mixed  with  another  kind  of  air  that 
extinguishes  flame  and  destroys  living  creatures,  so 
that  the  one  must  constantly  be  counteracting  the 
effects  of  the  other.” 

Humphry  racked  his  brains  for  a -long  time  for 
the  means  whereby  to  separate  the  two  kinds  of  air 
from  each  other.  At  last  he  remembered  one  of 
Lavoisier’s  experiments  in  connexion  with  the  sub- 
ject, and  immediately  set  to  work  to  repeat  it. 

With  this  view  the  lad  obtained  some  u calcined 
mercury,”  for  this  substance  he  knew  to  have  been 
produced  merely  by  burning  metallic  mercury  for  a 
long  time  in  a tube  exposed  to  the  air,  so  that  the 
portion  of  the  atmosphere  which  supported  com- 
bustion (instead  of  being  evolved  in  a gaseous  form, 
as  in  the  case  of  the  burning  charcoal)  had  become 
Jixed,  or  rendered  solid , in  the  “ calx  ” which  resulted 
from  the  process.  The  boy  was  therefore  anxious" 
to  see  whether  it  were  not  possible,  by  burning  the 
calcined  product  once  more,  to  drive  off  that  portion 
of  air  which  had  been  taken  up  by  it  during  the 
previous  burning,  and  so  to  discover  what  are  the 
peculiar  and  distinctive  properties  of  the  air  which 
had  been  absorbed.  Consequently,  he  submitted 
some  of  this  calcined  mercury  to  a red  heat  in  a 
retort,  and  collected  the  gas  that  was  given  off  from 
it  in  a wide-mouthed  bottle  from  which  he  had  cut 


THE  WONDERFUL  EFFECTS  OF  HEAT.  253 

off  the  bottom.  This,  having  corked,  he  filled  with 
water,  and  stood  on  a perforated  ledge  in  a pail — 
the  gas  being  collected  as  before  described.  When 
the  water  had  all  been  displaced  from  the  bottle, 
and  it  was  consequently  full  of  gas,  Humphry  slid 
it,  while  under  the  water,  off  the  ledge  into  a soup- 
plate,  and  then,  removing  it  to  a table,  proceeded  to 
investigate  its  properties. 

Here,  then,  he  had  a jar-ful  of  the  gas  (named 
oxygen  by  chemists)  that  maintained  the  combustion 
of  bodies  in  the  open  air,  and  separate,  too,  from 
the  other  gas,  which  tended  rather  to  retard  their 
burning  in  the  atmosphere. 

Humphry’s  first  experiment  was  to  introduce  into 
the  gas  thus  obtained  a lighted  taper,  placed  at 
the  end  of  the  wire  as  before,  and  the  boy  was 
enraptured  as  he  beheld  the  flame  immediately  en- 
large (instead  of  diminishing,  as  when  confined  in  a 
jar  of  mere  atmospheric  air),  and  become  intensely 
bright,  while  the  combustion  proceeded  at  so  rapid 
a rate  that  the  piece  of  taper  itself  was  soon  con- 
sumed. Then  another  piece  of  taper  was  used,  but 
this  was  blown  out  immediately  after  being  lighted, 
so  that  the  wick  was  merely  glowing  on  its  intro- 
duction into  the  gas.  On  being  plunged  into  the 
jar,  however,  it  was  instantly  re-kindled,  and  burst 
into  the  same  vivid  flame  as  before. 

Next,  the  combustion  of  sulphur  was  tried  in 
the  gas.  This  substance  burns  in  the  open  air. 


254 


THE  WONDERS  OF  SCIENCE. 


as  is  well  known,  with  a small  blue  flame.  On 
placing  a small  piece  of  lighted  sulphur,  however, 
in  a copper  capsule  attached  to  the  end  of  a long 
wire,  it  was  no  sooner  lowered  into  the  jar  than  it 
began  to  burn  with  a beautiful  purple  or  lilac- 
coloured  light,  the  flame  becoming  suddenly  en- 
larged, and  the  sulphur  itself  appearing  to  dissolve 
in  the  gas.  At  the  conclusion  of  the  experiment 
the  water  in  the  soup-plate,  in  which  the  jar  stood, 
was  set  carefully  on  one  side,  for  after-examina- 
tion. 

After  this  the  lad  tried  the  combustion  of  phos- 
phorus in  another  jar  of  gas,  in  the  same  man- 
ner. Humphry  knew  the  combustion  of  this  to 
be  very  vivid,  even  when  inflamed  in  the  atmos- 
phere ; so,  to  prevent  accidents,  he  used  in  the  jar 
a piece  not  larger  than  a pea : but  even  this,  when 
lowered  alight  into  the  gas,  produced  so  intensely 
white  a flame  that  he  could  scarcely  bear  to  look  at 
it,  while  clouds  of  white  flaky  matter  were  evolved 
from  it  like  smoke ; the  heat,  too,  was  so  great, 
that  he  was  afraid  the  jar  would  crack:  and  so  it 
would  have  done,  had  he  not,  luckily,  employed  a 
very  large  one. 

The  young  experimentalist  was  overjoyed  at  the 
splendour  of  the  combustion  of  these  substances, 
and  longed  to  see  whether  it  were  possible  to  burn 
the  metals  by  such  means.  So,  having  made  an- 
other jar-ful  of  the  same  gas,  and  placed  it  over 


THE  WONDERFUL  EFFECTS  OF  HEAT.  255 

some  water  in  a soup-plate,  he  took  a piece  of  watch- 
spring,  and  when  he  had  affixed  the  sulphur  tip  of  a 
match  to  the  end  of  this,  he  lighted  the  match  and 
plunged  the  whole  into  the  gas.  He  was  soon  well 
repaid  for  his  pains ; for  in  a short  while  the  met- 
al burst  into  vivid  combustion,  throwing  off  a 
shower  of  the  most  brilliant  sparks,  which  played 
around  it  like  a fountain  of  fire,  whilst  goutes  of  the 
white-hot  metal  fell  hissing  through  the  water,  and 
lay  beneath  it  for  some  time,  red  hot  upon  the  plate, 
the  glaze  of  which  was  afterwards  found  to  have 
been  even  fused  at  the  points  where  the  molten 
iron  had  fallen  upon  it. 

But  the  boy’s  rapture  on  beholding  the  wonder  of 
combustible  iron  was  not  altogether  unmingled  with 
fear ; for  the  heat  produced  by  the  burning  of  the 
metal  was  so  intense,  that  he  grew  nervous  lest  the 
glass  jar  should  break  during  the  experiment.  Pie 
was  wise  enough,  however,  to  hold  it  in  his  hand, 
so  as  to  allow  a little  of  the  gas  to  escape,  as  well  as 
to  prevent  the  jarring  of  the  glass  on  the  plate  be- 
neath. 

Humphry  was  now  nearly  exhausted  with  his 
labours,  and  it  was  time  to  reflect  upon  all  that  had 
occurred. 

In  the  first  place,  then,  it  was  certain  that  a con- 
siderable quantity  of  the  gas  used  in  these  experi- 
ments had  disappeared  during  the  combustion,  for 
the  water  had  each  time  risen  in  the  jar  above  the 


256 


THE  WONDERS  OF  SCIENCE. 


level  of  that  in  the  soup-plate.  “What,  then,  had 
become  of  the  lost  gas?”  he  asked  himself.  There 
was  but  one  answer — It  had  combined  with  the  burn- 
ing body , and  formed  a new  substance  with  it.  In  the 
case  of  the  burning  sulphur,  the  water  that  had 
been  in  the  soup-plate  below  the  jar  was  found, 
on  examination,  to  be  sour  to  the  taste,  and  to 
redden  vegetable-blue  colours ; so  that  here  the  gas 
had  combined  with  the  combustible  and  produced 
an  acid  that  was  soluble  in  water.  Again,  with 
the  burning  phosphorus,  the  white  flakes  that  had 
been  evolved  during  the  combustion  had  been 
ultimately  dissolved  by  the  water,  which  likewise 
tasted  sour,  while  it  stained  vegetable  colours  in  the 
same  manner  as  the  sulphur  product  did ; whereas, 
in  the  case  of  the  burning  iron,  the  metal  appeared 
to  have  been  rusted,  for  the  particles  remaining  at 
the  bottom  of  the  soup-plate  were  found,  after  the 
experiment,  to  have  lost  their  metallic  nature,  and 
to  have  assumed  all  the  character  of  a “ calxf  or 
rust. 

“Well,  then,”  said  the  lad,  “it  seems  that  during 
combustion  one  part  of  the  air  combines  with  the 
burning  bodies,  and  so  either  rusts  or  acidifies  them.” 
In  confirmation  of  this  view,  he  recollected  “ that 
the  gas  evolved  from  the  burning  charcoal  also 
gave  a slightly  sour  taste  to  the  water  it  passed 
through.” 

“ Still,”  mused  Humphry,  “if  a part  of  the  air 


THE  WONDERFUL  EFFECTS  OF  HEAT.  257 

really  does  combine  with  the  combustible  burning 
in  it,  the  result,  of  course,  should  be,  that  the  com- 
bustible, after  being  burnt,  should  be  heavier  than  be- 
fore— even  as  the  lime  with  which  I absorbed  the 
gas  from  the  burning  charcoal  became  greatly  in- 
creased in  weight  by  it.” 

The  youth  was  not  long  in  putting  this  part  of 
the  matter  to  a practical  test.  Having  accurate- 
ly weighed  a small  quantity  of  calcined  mercury 
(which,  as  we  said  before,  he  knew  to  be  a rust  of 
the  metal),  he  set  to  work  again  to  make  it  red  hot, 
and  to  drive  off  the  air  with  which  it  had  previous- 
ly been  made  to  combine  while  burning.  This  gas 
he  collected  in  a small  glass  jar,  open  at  the  bottom, 
and  having  a stop-cock  at  the  top  of  it.  Then  the 
boy  took  a thin  hollow  ball  of  glass,  which  had  also 
a stop-cock  fitted  to  it.  Having  screwed  this  on  to 
the  metal  plate  of  his  air-pump,  he  exhausted  the 
glass  ball  as  entirely  of  air  as  he  could,  and  then 
closing  the  cock  he  detached  it  from  the  pump, 
and  proceeded  to  ascertain  the  weight  of  the  ball 
now  that  it  was  divested  of  air.  This  done,  Hum- 
phry screwed  the  stop-cock  of  the  glass  ball  on  to 
that  of  the  glass  jar  in  which  he  had  collected  the 
gas  from  the  calcined  mercury  ; then,  turning  on 
both  the  cocks,  the  gas  rose  from  the  jar  into  the 
ball,  and  when  the  jar  itself  was  full  of  liquid,  and 
all  the  gas  had  consequently  been  removed  from  it, 
he  closed  the  stop-cock  once  more,  and,  unscrewing 

R 


25  8 


THE  WONDERS  OF  SCIENCE. 


the  glass  ball  from  the  jar,  proceeded  to  ascertain 
how  much  the  ball  had  gained  in  weight,  now  that 
it  contained  the  whole  of  the  gas  evolved  from  the 
calcined  mercury. 

The  next  step  was  to  weigh  the  mercury  itself* 
This,  however,  was  no  longer  the  red  powder  that 
it  was  before  the  gas  had  been  driven  off  from  it, 
but  had  now  become  “■  reduced”  into  so  much  bright 
liquid  metal ; and  on  being  put  into  the  scales  it 
was  found  to  have  lost  just  as  many  grains  in  weight 
as  the  gas,  which  had  been  collected  from  it,  required 
to  balance  it  in  the  scales. 

But  this  was  not  enough  to  satisfy  the  cautious 
young  experimentalist,  for  he  still  desired  to  see 
whether,  if  the  same  quantity  of  metallic  mercury 
were  burned  in  the  same  quantity  of  gas,  the  re- 
sulting compound  of  the  metal  and  the  air  would 
weigh  exactly  as  much  as  the  air  and  the  metal  did 
separately. 

Accordingly,  Humphry  proceeded  now  to  burn 
the  metallic  mercury  in  the  gas,  and  so  to  cause 
them  to  combine  once  more.  By  keeping  the  metal 
at  a red  heat  with  the  gas  above  it,  the  combination 
was  at  length  effected,  and  then,  on  weighing  the 
red  u calx,”  or  rust,  that  resulted  from  the  process, 
it  was  ascertained  to  be  precisely  as  heavy  as  the 
metal  and  the  gas  had  weighed  when  separate. 

Here,  then,  it  was  manifest  that  substances  by 
burning  were  increased  in  weighty  and  that  they  were 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


259 


just  as  much  heavier  after  combustion  as  the  weight  of  the 
quantity  of  air  which  had  been  absorbed  by  them  during 
the  process. 

“Is  it  true,  therefore,”  mused  the  boy,  “ that  the 
candle  and  the  coals,  which  appear  to  us  to  be  de- 
stroyed by  combustion,  become  positively  increased 
in  weight  by  it  V’ 

The  experiment  which  Humphry  had  already 
performed  in  collecting  the  gas  from  burning  char- 
coal assured  him  that  such  was  positively  the  case, 
for  he  knew  that  this  gas,  though  invisible,  had  an 
absolute  weight,  being  so  much  heavier  than  the  at- 
mosphere that  it  admitted  of  being  poured,  like  wa- 
ter, from  one  vessel  to  another.  The  experiment 
with  the  calcined  mercury,  moreover,  told  him,  that 
if  he  had  weighed  the  charcoal  before  it  was  burnt, 
as  well  as  the  quantity  of  air  which  it  had  con- 
sumed while  burning,  he  would  have  found  the  whole 
of  the  gas  which  resulted  from  the  combustion  would 
have  been  precisely  as  heavy  as  the  air  and  the  char- 
coal added  together. 

For  the  same  reason,  if  the  gases  evolved  from  a 
burning  candle  were  to  be  collected,  they,  likewise, 
would  be  found  to  be  heavier  than  the  candle  it- 
self; and  just  as  much  heavier,  too,  as  the  quan- 
tity of  air  which  had  disappeared  during  the  com- 
bustion. 

Combustion , therefore , was  merely  the  rapid  combi- 


260 


THE  WONDERS  OF  SCIENCE. 


nation  of  a portion  of  the  air  with  a combustible  bodyy 
accompanied  with  the  evolution  of  heat  and  light. 

Still  Humphry  could  not  quit  the  subject  without 
examining  the  conditions  which  were  necessary  to 
produce  such  a combination.  The  principal  requi- 
site ivas  manifestly  elevation  of  temperature. 

Some  substances,  however,  inflame  at  ordinary 
temperatures — immediately  on  entering  the  atmos- 
phere— as,  for  instance,  the  gas  called  “ phosphuret- 
ted  hydrogen.”  This  was  a new  discovery  in  young 
Humphry’s  time,  and  the  boy  delighted  to  produce 
the  gas  by  heating  a small  quantity  of  phosphorus  in 
a retort  completely  filled  with  a moderately  strong 
solution  of  caustic  potash — the  heat  being  carefully 
applied  until  the  solution  boiled,  while  the  beak  of 
the  retort  was  kept  under  the  shelf  of  a water-bath. 
Upon  coming  into  contact  with  the  air,  Humphry 
saw  the  bubbles  of  gas,  as  they  left  the  surface  of 
the  water,  suddenly  inflame,  with  a slight  explosion ; 
and  as  the  atmosphere  was  still,  each  bubble,  on 
bursting,  produced  a beautiful  expanding  ring  of 
white  smoke. 

It  is  this  gas  which  gives  rise  to  the  production 
of  those  lights  in  the  air  which  are  known  by  the 
names  of  “ ignes  fatuT  (“ will-o'-the-wisps ,”  or  u Jaclc- 
d-lanterns  f)  and  “ corpse-candles ” — the  former  ap- 
pearing over  marshes,  and  the  latter  being  seen  to 


THE  WONDERFUL  EFFECTS  OF  FIE  AT.  261 

rise  from  recent  graves — but  both  alike  proceeding 
from  the  decomposition  of  organic  matter.* 

Again,  phosphorus  dissolved  in  sulphuret  of  carbon 
produces  a spontaneously  inflammable  solution ; so 
that  if  a small  quantity  of  the  liquid  be  poured  on 
a piece  of  paper  it  evaporates  rapidly,  and  leaves 
the  phosphorus  behind,  which  immediately  bursts  into 
flame. 

The  same  phenomenon  of  spontaneous  combus- 
tion also  occurs  with  the  substance  called  “ pyro - 
phorus .”  This  is  generally  formed  of  powdered  alum 
heated  with  an  equal  weight  of  brown  sugar  or 
honey.  After  the  materials  have  been  melted  and 
well  mixed  in  an  iron  ladle,  they  are  made  red  hot 
in  a phial  coated  with  clay,  and  placed  in  a cru- 
cible of  sand — the  heating  process  being  continued 
until  a blue  flame  appears  at  the  mouth  of  the  hot-, 
tie ; this  is  allowed  to  burn  for  about  five  minutes, 
when  the  phial  is  well  stopped  and  removed  from  the 
fire. 

The  compound,  on  being  cooled  and  exposed  to 
the  air,  is  spontaneously  combustible. 

Sulphate  of  potassa,  likewise,  when  heated  to  red- 
ness with  half  its  weight  of  lamp-black,  forms  a 
compound,  which  takes  fire  immediately  on  expo- 
sure to  air. 

* A chemical  philosopher  in  America  ignited  a piece  of  paper 
by  one  of  these  lights  on  a still  night.  The  breath,  however,  had 
to  be  held  during  the  operation,  for  the  least  agitation  of  the  air 
wrafted  them  from  the  spot. 


262 


THE  WONDERS  OF  SCIENCE. 


Again,  tartrate  of  lead , heated  to  a dull  red  in  a 
glass  tube,  forms,  when  cool,  a very  perfect  pyropho- 
rus,  which  immediately  inflames  on  being  shaken  out 
into  the  atmosphere.  F urther,  when  iron  is  in  a state 
of  extreme  mechanical  division — such  as  very  fine  pow- 
der— its  affinity  for  the  oxygen  of  the  atmosphere 
is  such  that  it  heats,  and  even  ignites,  on  exposure 
to  the  air.  This  is  the  case  with  the  finely-divided 
metal  as  obtained  by  the  action  of  hydrogen  gas 
upon  red-hot  iron-rust,  so  that,  when  suffered  to  cool 
in  this  gas,  the  iron  is  as  spontaneously  oxidizable 
as  even  potassium  itself. 

Moreover,  if  a small  piece  of  spongy  platinum  be 
held  in  a jet  of  hydrogen,  issuing  from  a small 
tube  into  the  atmosphere,  the  platinum  immediate- 
ly becomes  red  hot,  while  the  gas  itself  bursts  into 
flame. 

Platinum  wire , or  foil,  if  the  surface  be  perfect- 
ly clean,  acts  so  rapidly  at  common  temperatures 
on  a mixture  of  oxygen  and  hydrogen  gases  (mixed 
in  the  proportion  of  1 to  2),  that  it  often  becomes 
red  hot  on  being  introduced  into  a vessel  contain- 
ing them,  and  kindles  the  mixture.  Handling  the 
platinum,  however,  wiping  it  with  a towel,  or  ex- 
posing it  to  the  atmosphere  for  a few  days,  suffices 
to  soil  the  surface  of  the  metal,  and  so  to  prevent 
its  action. 

Finally,  a piece  of  the  metal  called  potassium 
(procured  from  potash ) has  so  strong  an  affinity  for 


THE  WONDERFUL  EFFECTS  OF  HEAT.  263 

oxygen,  that  when  thrown  upon  water,  at  ordinary 
temperatures,  the  metal  decomposes  it  the  instant 
it  touches  the  liquid,  and  so  much  heat  is  disen- 
gaged that  the  potassium  is  inflamed,  and  burns  viv- 
idly while  swimming  on  the  surface.  The  same 
spontaneous  combustion  ensues,  indeed,  with  ice — 
so  that  the  cold  body  appears  to  heat  the  metal  even 
to  inflammation. 

But  a still  more  curious  instance  of  spontaneous 
inflammation  is  to  be  found  in  the  sudden  explosion 
of  a mixture  of  Chlorine  and  Hydrogen  gases  when 
exposed  to  sunshine ; for  though  the  two  gases,  when 
mixed  together  in  equal  volumes,  may  be  preserved 
•without  change  in  a dark  place  for  any  length  of 
time,  nevertheless,  immediately  they  are  submitted 
to  the  direct  solar  rays,  the  whole  mixture  be- 
comes suddenly  inflamed,  and  a violent  explosion 
ensues. 

Next  to  those  substances  which  are  spontane- 
ously combustible  comes  phosphorus , which  inflames, 
when  perfectly  dry,  at  the  low  temperature  of  60°. 
Indeed,  such  is  its  tendency  to  combine  with  the 
air,  that,  if  free  from  all  moisture,  it  takes  fire 
by  the  heat  of  the  hand  alone.  Slight  friction,  as 
when  rubbed  upon  a piece  of  coarse  paper,  also  pro- 
duces the  same  result.  It  is  very  difficult,  how- 
ever, to  light  a piece  of  paper  by  the  flame  of  phos- 
phorus, for  the  paper  becomes  coated  with  a crust 
of  the  solid  phosphorous  acid , which  is  produced  by 


264 


THE  WONDERS  OF  SCIENCE. 


the  combustion,  and  serves  to  protect  it  from  the 
flame. 

There  is,  likewise,  a gas  (for  the  knowledge  of 
which  we  are  indebted  to  the  after-discoveries  of 
Davy  himself),  called  protoxide  of  chlorine , which 
requires  so  slight  an  elevation  of  temperature  to 
decompose  it,  that  even  the  heat  of  the  hand  is 
sufficient  to  cause  it  to  explode  with  the  evolution 
of  heat  and  light.  This  gas  is  produced  by  the 
action  of  hydrochloric  acid  on  chlorate  of  potash 
and  water,  and  it  is  so  explosive  that  it  frequent- 
ly detonates  violently  in  being  transferred  from  one 
vessel  to  another.  It  should,  therefore,  be  dealt 
with  by  none  but  experienced  chemists.  A small 
piece  of  phosphorus  let  up  into  it  instantly  takes 
fire,  and  burns  with  much  brilliancy.  Sulphur  like- 
wise decomposes  it  with  violent  detonation,  and  even 
a piece  of  blotting-paper  introduced  into  the  gas  is 
sufficient  to  cause  it  to  be  suddenly  resolved  into  its 
elements. 

The  gas  termed  Binoxide  of  Chlorine  (called  also 
the  Peroxide ) is  even  more  explosive  than  the  Pro- 
toxide. It  detonates  violently  when  heated  to  212°, 
emits  a strong  light,  and  undergoes  a greater  expan- 
sion then  the  simple  oxide  above  described. 

Again,  the  Binoxide  of  Hydrogen  (or  Peroxide , 
as  it  is  sometimes  denominated),  when  heated  to 
212°,  gives  off  oxygen  so  rapidly  as  to  cause  an 
explosion,  while  the  rusts  (oxides)  of  some  of  the 


THE  WONDERFUL  EFFECTS  OF  HEAT.  265 

metals  act  upon  it  with  such  energy,  that,  when 
dropped  into  it,  a violent  detonation  immediately 
ensues,  and  the  glass  tube  on  which  the  experiment 
is  conducted  becomes  red  hot. 

F urther,  the  gas  called  Binoxide  of  Nitrogen , when 
combined  with  sulphurous  acid  gas,  produced  a com- 
pound called  Nitro-sidphuric  Acid,  which  is  so  prone 
to  decomposition  that  it  cannot  be  collected  in  a 
separate  state,  and  the  salts  of  which  are  held  togeth- 
er with  such  slight  affinity  that  even  a little  charcoal 
powder,  or  spongy  platinum,  is  sufficient  to  cause  a 
violent  evolution  of  gas,  while  at  a temperature  only 
a few  degrees  above  that  of  boiling  water,  an  explo- 
sion ensues. 

Moreover,  the  Bisulphuret  (called,  also,  the  Per - 
sulphuret)  of  Hydrogen , which  is  a yellow  oil-like 
liquid,  has  its  elements  so  feebly  united,  that  at  a 
heat  short  of  212°  it  is  instantaneously  resolved 
into  sulphur , and  the  simple  Sulphuretted  Hydrogen 
which  is  evolved  in  the  form  of  gas,  with  almost 
explosive  violence.  The  same  effect  is  produced  by 
the  mere  contact  of  most  substances — especially  the 
metals,  flint,  and  even  the  earths  in  powder — while 
the  oxides  of  gold  and  silver  are  “reduced”  by  it 
with  such  energy  that  they  are  rendered  instanta- 
neously red  hot. 

These  binary  compounds  of  oxygen  or  sulphur 
have  most  of  them  been  discovered  since  Davy’s 
time.  They  are,  however,  remarkable  in  possessing 


266 


THE  WONDERS  OF  SCIENCE. 


kindred  affinities,  and  being  severally  decomposible 
at  a temperature  of  212°. 

After  these,  in  the  order  of  ready  decomposibili- 
ty,  come  the  compounds  of  Nitrogen. 

The  peculiar  black  powder,  called  by  chemists 
iodide  of  nitrogen , which  is  produced  by  pouring 
some  strong  ammonia  upon  a very  small  quantity  of 
iodine,  is  so  explosive,  that  it  detonates  violently 
as  soon  as  it  is  dried ; and  the  slightest  pressure, 
even  when  moist,  produces  a similar  effect.  If 
put  into  pure  ammonia,  it  explodes  when  lightly 
pressed  in  that  liquid.  Heat  and  light  are  emitted 
during  the  detonation,  which  is  merely  a species  of 
instantaneous  combustion.  So  dangerous  is  this 
compound,  that  the  most  experienced  chemists  sel- 
dom operate  on  more  than  a few  grains  of  iodine  at 
once. 

The  yellow  oil-like  liquid,  called  chloride  of  ni- 
trogen, which  results  from  the  action  of  chlorine  gas 
upon  sal  ammoniac,  also  enters  into  instantane- 
ous combustion  at  very  low  temperatures  ; so  that, 
when  it  is  heated  to  a little  above  200°,  it  detonates 
with  tremendous  violence,  a vivid  flash  of  light 
being  produced  at  the  same  time,  while  the  vessel 
— which,  to  prevent  accidents,  is  covered  with  a 
wire  cage — is  broken  to  atoms.  This  compound  is 
so  dangerous,  being  one  of  the  most  explosive  sub- 
stances yet  known,  that  in  dealing  with  it  the  face 
is  always  protected  by . a mask,  and  only  a small 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


267 


globule  of  it,  no  larger  than  a mustard  seed,  ex- 
perimented upon.  Dulong,  the  French  chemist 
who  discovered  it,  lost  an  eye  and  the  use  of  a 
finger  whilst  operating  with  it ; and  Davy  him- 
self, in  after-life,  was  wounded  in  the  face  by  the 
effects  of  its  detonation.  The  mere  contact  of  this 
substance  with  certain  combustibles  causes  it  to 
explode  violently,  even  under  water,  at  ordinary 
temperatures.  If  touched  with  phosphorus,  India 
rubber,  common  oil,  turpentine,  caustic  potash,  or 
even  soap,  it  detonates  so  violently  as  to  break  to 
pieces  the  vessel  containing  it,  and  to  scatter  the 
water  in  which  it  is  immersed  in  a shower  all 
around. 

Bromide  of  nitrogen , again,  is  said  to  be  even 
more  easily  decomposed  than  the  chloride.  It  is  a 
dark-red  oily  liquid,  having  a foetid  odour,  and  giv- 
ing off  a vapour  that  is  very  irritating  to  the  eyes. 
This  compound,  when  touched  with  phosphorus,  or 
even  a small  piece  of  arsenic,  detonates  with  tremen- 
dous violence. 

Next  to  the  above  remarkable  compounds  of 
Nitrogen,  the  fulminates  of  the  precious  metals 
(into  the  composition  of  which,  however,  Nitrogen 
also  enters)  must  be  ranked  in  the  order  of  ready 
combustibility ; for  these  likewise  explode  at  very 
low  temperatures,  with  the  production  of  heat  and 
light. 

First  come  the  Nitrurets  of  Mercury  and  Silver 


268 


THE  WONDERS  OP  SCIENCE. 


— that  is  to  say,  compounds  of  those  metals  with 
Nitrogen.  These  are  formed  by  the  action  of  Am- 
monia on  the  oxide  of  Mercury  or  Silver.  The 
Nitruret  of  Silver  explodes  with  tremendous  violence 
when  gently  rubbed  or  heated,  and  the  Nitruret  of 
Mercury  when  struck  with  a hammer,  or  acted  upon 
by  strong  oil  of  vitriol. 

Fulminating  Gold , when  suddenly  heated  to 
about  290°,  detonates  with  great  force  and  a 
vivid  flash ; and  if  exploded  upon  platinum  foil, 
the  metal  is  torn  at  the  point  of  contact.  Friction 
with  hard  bodies,  or  an  electric  shock,  also  ex- 
plodes it.  The  more  it  is  washed  and  dried,  the 
more  explosive  this  compound  becomes  ; and  if 
long  retained  at  the  temperature  of  boiling  water, 
so  as  to  become  perfectly  dry,  the  slightest  friction 
causes  it  to  detonate  immediately  and  violently. 
If  it  be  moist,  however,  it  does  not  explode  on 
the  application  of  heat  till  dried,  and  those  portions 
which  first  become  dry  explode  the  sqonest;  so 
that,  in  such  a case,  a succession  of  detonations  is 
produced. 

Fulminating  Mercury  requires  a temperature  of 
300°  to  cause  it  to  explode,  which  it  then  does 
with  a bright  flame.  It  also  detonates  by  friction, 
so  that  the  greatest  caution  is  required  in  pre- 
paring and  dealing  with  it.  This  compound  has 
even  been  known  to  explode  in  a moist  state,  and 
in  the  most  careful  and  skilful  hands  it  cannot 


THE  WONDERFUL  EFFECTS  OF  HEAT.  269 

be  touched  without  considerable  danger.*  This  is 
the  substance  used  in  the  percussion  caps ; it  is 
introduced  into  the  caps  moistened  with  a little 
tincture  of  benzoin,  so  as  to  be  dropped  into  them, 
and  then  carefully  dried.  Howard,  the  discoverer 
of  the  compound,  endeavoured  to  substitute  it  for 
gunpowder,  but  the  explosion  was  found  to  be  so 
sudden  that  it  burst  the  gun  without  expelling  the 
shot. 

Fulminating  Silver  likewise  explodes,  with  the  ev- 
olution of  light  and  heat,  at  nearly  the  same  low 
temperature.  A grain,  or  merely  half  a grain  of 
this  substance,  detonates  with  great  violence,  when 
heated  or  when  touched  with  any  hard  body.  On 
being  placed  upon  a piece  of  rock  crystal,  and 
rubbed  in  the  slightest  manner  by  another  crys- 
tal, it  explodes  with  great  force.  It  has  sometimes 
exploded  upon  the  contact  of  a glass  rod,  even  un- 
der water ; so  that  merely  the  feather  of  a common 
quill  is  generally  used  to  collect  it.  It  is  danger- 
ous to  keep  it  in  a cork-stoppered  phial,  for  serious 


* A melancholy  proof  of  this  was  furnished  by  the  death  of 
Mr.  Hennell  (the  chemist  at  Apothecaries’  Hall)  on  the  4th  June, 
1842.  He  was  in  the  act  of  mixing  twro  separate  portions  of  the 
powder  in  a moist  state  with  an  ivory  knife,  when  the  whole 
quantity,  amounting  to  above  6 lbs.  exploded,  and  shattered  his 
head,  breast,  and  right  arm  to  atoms.  A man,  however,  who 
was  standing  within  four  yards  of  him,  was  not  injured,  but  the 
windows  of  the  surrounding  buildings  were  broken ; while  a 
large  wooden  block,  upon  which  one  of  the  basins  was  placed, 
was  shivered,  as  was  also  the  pavement  on  which  it  stood. 


270 


THE  WONDERS  OF  SCIENCE. 


accidents  have  arisen  from  its  unexpected  explosion 
in  a confined  state.  In  short,  persons  cannot  be  toe 
careful  in  meddling  with  it,  and  its  use  for  detona> 
ting  balls  and  other  purposes  of  amusement  is  high-> 
1 y perilous  and  reprehensible. 

Fulminating  Platinum , on  the  other  hand,  ex- 
plodes at  a temperature  of  420°  with  a loud  re- 
port. 

There  is  likewise  a fulminating  powder , com- 
posed of  a mixture  of  3 parts  nitre  with  1 of  sul- 
phur, and  2 of  dry  carbonate  of  potash.  This  sub- 
stance explodes  with  much  violence  at  the  low  tern- 
perature  of  330° ; so  that  if  a little  of  the  com- 
pound be  heated  up  to  that  point  upon  a metallic 
plate,  it  blackens,  fuses,  and  detonates  with  great 
force. 

Again,  a mixture  of  3 parts  chlorate  of  potash 
and  1 of  sulphur  detonates  loudly  when  struck 
upon  an  anvil  with  a hammer,  and  even  sometimes 
explodes  spontaneously.  If  2 or  3 grains  of  chlo- 
rate of  potash  be  reduced  to  powder  in  a mor- 
tar, and  some  very  fine  flour  of  brimstone  be  then 
added  to  it,  the  two  substances,  when  rubbed  to- 
gether, will  detonate  with  a smart  noise,  like  the 
cracking  of  a whip.  A mixture  of  chlorate  of 
potash  and  sulphuret  of  antimony  takes  fire  by 
gentle  trituration,  and  deflagrates  with  a bright 
puff  of  flame  and  smoke.  Chlorate  of  potash  was 
proposed  by  Berthollet  (the  French  chemist)  as  a 


THE  WONDERFUL  EFFECTS  OF  HEAT.  271 

substitute  for  nitre  in  gunpowder.  The  attempt 
was  made  at  Essone,  in  1778  ; but  no  sooner  was 
the  mixture  of  the  chlorate  with  the  sulphur  and 
charcoal  submitted  to  trituration  than  it  exploded 
with  violence,  and  proved  fatal  to  several  persons. 

With  phosphorus  and  chlorate  of  potash  the  ex- 
plosion is  dangerously  violent : 1 grain  of  phospho- 
rus with  two  of  the  chlorate,  if  placed  in  a small 
piece  of  paper  and  struck  with  a hammer  upon  an 
anvil,  will  immediately  explode,  and  the  phospho- 
rus be  thrown  about  in  an  inflamed  state.  Gun- 
powder, again,  if  mixed  with  powdered  glass  and 
struck  with  a heavy  hammer  upon  an  anvil,  almost 
always  explodes. 

Moreover,  a mixture  of  oxygen  and  hydrogen  gases , 
suddenly  submitted  to  violent  mechanical  compres- 
sion, unite  with  a vivid  flash  of  light  and  produce 
water. 

Next  to  Phosphorus  and  the  Fulminates,  Sul- 
phur is  the  most  easily  kindled.  This  body  enters 
into  combustion  at  about  500°.  It  is  the  compara- 
tively low  temperature  at  which  sulphur  bursts  into 
flame,  that  makes  it  so  important  an  ingredient  in 
gunpowder,  matches,  &c.  The  easy  combustibility 
of  sulphur  may  be  well  illustrated  by  propelling  a 
small  quantity  of  it  in  powder  into  the  current  of 
hot  air  issuing  from  the  glass  chimney  of  a gas  lamp, 
when  it  will  be  seen  to  take  fire  at  a considerable 
height  above  the  flame. 


272 


THE  WONDERS  OF  SCIENCE. 


* 

Wood,  cotton,  paper,  &c.  require,  on  the  other 
hand,  their  temperatures  to  be  raised  much  higher 
than  that  required  for  the  inflaming  of  sulphur, 
in  order  to  be  made  to  enter  into  combustion.* 
Paper  merely  becomes  brown  or  scorched  at  the 
heat  of  440°,  nor  can  it  be  lighted  at  a red  heat, 
though  the  temperature  of  this  is  1000°.  Cotton 
or  tow,  however,  when  greased  with  oil,  occasionally 
absorbs  air  so  rapidly,  and  produces  so  much  heat 

* In  the  ordinary  lucifer-match  (an  invention  since  Davy’s 
time)  we  have  a striking  illustration  of  the  different  temperatures 
required  for  various  substances  to  enter  into  combustion.  The 
phosphorus  writh  w'hich  these  lucifers  are  tipped  becomes  in- 
flamed at  a very  low  heat  (GO0),  so  that  mere  friction  is  sufficient 
to  ignite  it.  This  substance,  in  burning,  produces  heat  sufficient 
to  kindle  the  sulphur  next  to  it ; for  this,  as  we  have  seen, 
enters  into  combustion  at  about  500°  ; and  the  sulphur  again, 
in  burning,  raises  the  temperature  sufficient  to  ignite  the  wood, 
which  requires  a heat  of  at  least  1000°  before  it  can  be  made  to 
burn.  Had  the  match  been  tipped  with  phosphorus  alone,  the 
phosphorous  acid  produced  by  the  combustion  would  have  in- 
crusted  the  wood  and  prevented  it  inflaming.  Before  the  use  of 
phosphorus  matches  had  become  general,  others  were  introduced, 
the  tips  of  which  wTere  coated  with  a mixture  of  chlorate  of  pot- 
ash and  sulphur,  and  these  had  to  be  drawm  forcibly  through  a 
piece  of  folded  sand-paper,  for  this  mixture  requires  a much  high- 
er heat  in  order  to  inflame  it.  Previous  to  the  introduction  of 
these,  again,  the  common  brimstone  match  was  in  general  use. 
This,  as  is  well  know'n,  was  kindled  by  means  of  a spark  in  tin- 
der— the  tinder  consisting  of  charred  rag,  and  the  spark,  there- 
fore, being  merely  a particle  of  charcoal  at  a red  heat,  while  the 
ignition  of  the  tinder  itself  was  originally  produced  by  the  per- 
cussion of  a piece  of  flint  and  steel,  w'hich  evolved  so  much  heat 
that  small  splinters  of  the  metal  were  fused  by  it  and  fell  upon 
the  tinder  in  a red-hot  state. 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


273 


during  the  process,  that  spontaneous  combustion  fre- 
quently occurs  from  this  cause.  The  same  effect 
sometimes  arises  from  hay  being  stacked  before  be- 
ing perfectly  dry ; the  moisture  sets  up  a kind  of 
fermentation  in  the  interior  of  the  stack,  and  this 
evolves  so  much  heat  that  the  temperature  becomes 
raised  to  the  point  required  for  the  material  to  en- 
ter into  rapid  combination  with  the  atmosphere,  so 
that  spontaneous  combustion  is  the  result. 

Again,  there  are  certain  mixtures  of  gases  which 
are  explosible  at  a red  heat,  while  others  cannot  be 
made  to  enter  into  combustion  at  that  temperature, 
but  require  the  presence  of  flame  in  order  to  fire  them. 

Carhuretted  hydrogen  ( coal  gas),  sulphuretted  hy- 
drogen, and  carbonic  oxide , can  be  made  to  inflame 
in  air  by  red-hot  iron  or  charcoal ; and  a mix- 
ture of  oxygen  and  hydrogen  gases  can  be  exploded 
by  a red  heat  visible  in  daylight,  whereas  a dull  red 
heat  only  causes  the  two  gases  to  combine  silent- 
ly without  detonation.  Fire-damp , however,  (which 
is  light  carburetted-hydrogen  gas,  and  the  same  as 
that  which  rises  from  stagnant  pools  on  disturbing 
the  mud  at  the  bottom),  cannot  be  inflamed  by 
the  strongest  red  heat ; so  that  a fire  made  of  char- 
coal, that  will  burn  without  flame,  may  be  blown 
up  to  whiteness  without  exploding  a mixture  of 
this  gas  with  air.  A piece  of  iron  also,  at  the 
highest  degree  of  red  heat,  and  even  at  an  ordinary 
white  heat,  does  not  inflame  an  explosive  mix- 


274 


THE  WONDERS  OF  SCIENCE. 


ture  of  f re-damp,  but  when  brought  to  its  highest 
point  of  white  heat,  iron  immediately  causes  the  fire- 
damp to  combine  with  the  air  with  a violent  detona- 
tion. 

The  knowledge  of  this  fact,  which  we  owe  to  the 
researches  of  Davy  himself,  was  of  immense  import- 
ance in  the  construction  of  the  safety-lamp,  and,  once 
discovered,  it  was  treasured  in  the  brain  for  after 
use,  for  the  preservation  of  life  and  the  mitigation 
of  suffering. 

Again,  there  are  some  substances  which  are  so 
readily  inflammable  that  they  take  light  even  at  the 
approach  of  flame.  These  bodies  consist  of  highly 
vaporizable  liquids,  such  as  alcohol , ether,  naphtha , 
sulphur et  of  carbon , oil  of  turpentine , &c.  From  the 
tendency  of  these  combustible  liquids  to  pass  into 
vapour,  the  surrounding  atmosphere  (immediately 
on  opening  any  vessels  containing  them)  becomes 
charged  with  their  fumes,  so  that  an  almost  explosive 
mixture  is  formed  with  the  air ; and  as  this  extends 
to  some  distance  from  the  liquid  itself,  the  approach 
of  a lighted  body  instantaneously  causes  the  whole 
volume  of  vapour  to  pass  into  one  sheet  of  flame — 
an  effect  which  is  occasionally  attended  with  the  most 
disastrous  results. 

On  the  other  hand,  some  combustible  liquids  re- 
quire their  temperatures  to  be  highly  raised  before 
they  can  be  inflamed  ; such  is  the  case  with  the 
common  fixed  oils — as  lamp-oil,  and  others.  For 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


275 


this  purpose  a cotton  wick  is  usually  employed  in 
burning  them,  so  that,  by  the  capillary  attraction 
of  the  fibres,  a small  portion  of  the  liquid  may  be 
raised  above  the  level  of  the  rest,  and  the  oil  thus 
be  brought  into  connexion  with  the  flame  by  mi- 
nute quantities  at  a time ; the  consequence  being 
that,  as  each  small  portion  of  the  liquid  is  heated, 
it  is  converted  into  vapour,  or  gas — and  this,  by  the 

high  temperature  maintained  by  the  burning  wick, 

/ 

is  made  to  enter  into  combustion  with  the  surround- 
ing air,  and  so  to  be  continually  inflamed  above  it. 
Any  porous  substance  which  is  a bad  conductor  of 
heat  (such  as  Bath-brick  or  sandstone),  will,  if  cut 
to  a fine  edge,  answer  all  the  purposes  of  the  ordi- 
nary cotton  lamp-wick ; for  if  a light  be  applied  to 
this,  so  as  to  raise  its  temperature  sufficient  to  con- 
vert into  gas  the  film  of  oil  at  the  summit,  the  fluid 
will  be  readily  inflamed,  and  continue  burning  until 
such  an  incrustation  of  charcoal  ensues  at  the  tip  as 
to  prevent  the  oil  being  heated  any  longer  by  the 
flame. 

Further,  some  substances  cannot  be  made  to  burn 
at  ordinary  temperatures  in  the  open  air,  though,  on 
being  confined  in  a vessel  of  oxygen  gas,  they  readi- 
ly enter  into  combustion  when  their  temperature  is 
raised.  This  is  the  case,  as  we  have  seen,  with  iron, 
and  some  of  the  other  metals. 


The  next  problem  to  be  resolved  was,  Whence 


27b 


THE  WONDERS  OF  SCIENCE. 


come  the  light  and  heat  that  are  emitted  during  the 
process  of  combustion  ? 

“All  cases  of  combination  with  oxygen,”  mused 
the  youth,  “ such  as  the  rotting  of  wood,  and  the 
gradual  rusting  of  metals  in  the*open  air,  are,  prob- 
ably, attended  with  the  evolution  of  heat ; but 
in  such  instances  the  process  is  so  slow,  that  the 
heat  evolved  is  unobserved,  and  dissipated  without 
accumulation.  When  the  combination,  however, 
takes  place  in  a shorter  time,  as  in  the  production 
of  vinegar,  the  heat  becomes  proportionately  sensi- 
ble ; and  when  the  combination  with  the  oxygen  is 
so  rapid  that  the  whole  of  the  heat  is  evolved  in 
a much  more  limited  period,  as  during  combus- 
tion, the  increase  of  temperature  is  rendered  consid- 
erably mpre  intense.  A pound  of  charcoal,  for  in- 
stance, combining  with  oxygen  in  the  process  of  res- 
piration, gives  off  the  same  amount  of  heat  as  it  does 
when  in  a state  of  ignition,  and  takes  up  precise- 
ly the  same  quantity  of  the  gas.  In  the  one  case, 
however,  the  combination  is  spread  over  30  hours, 
whereas  in  the  other  it  occupies  but  as  many  min- 
utes.” 

Humphry  reflected  for  a long  time  as  to  the  ori- 
gin of  the  light  and  heat  evolved  during  the  burning 
of  substances. 

“Are  the  light  and  heat,”  said  he  to  himself, 
“ originally  imprisoned,  as  it  were,  in  the  com- 
bustible, and  set  free  during  the  burning  of  it? 


THE  WONDERFUL  EFFECTS  OF  HEAT.  277 

or  are  they  merely  the  result  of  the  rapid  and  ener- 
getic combination  of  the  oxygen  of  the  air  with  the 
burning  substance ?” 

The  former  assumption  the  boy  knew  to  be  La- 
voisier’s theory  of  the  subject,  but  such  an  expla- 
nation appeared  to  him  to  be  inconsistent  with  the 
facts. 

The  products  of  combustion  are  not  always  the 
same.  In  some  cases  they  consist  of  gases , as  in  the 
burning  of  Charcoal  and  Sulphur,  &c. ; in  others, 
liquids  are  produced,  as  by  the  combustion  of  oxygen 
and  hydrogen  gases,  the  product  in  that  case  being 
merely  water ; while  in  others,  again,  a solid  prod- 
uct is  the  result — as  when  phosphorus  is  burnt  a 
white  solid,  called  “ phosphorous  acid,”  being  then 
formed : and  so  with  zinc,  the  combustion  of  which 
produces  a solid  white  rust,  or  oxide. 

“Now,  if  the  heat  evolved  during  combustion,” 
thought  Humphry,  “proceeds  from  the  liberation 
of  the  latent  caloric,  or  that  which  previously  ex- 
isted in  the  substances  in  an  insensible  state,  it  would 
follow  that  such  heat  should  be  given  off  only  when 
the  combustibles  pass  from  a rarer  to  a denser 
form ; as,  for  instance,  when  water  is  produced  by 
the  burning  of  its  two  constituent  gases,  or  when 
the  oxygen  of  the  atmosphere  becomes  fixed  in 
some  solid  product,  as  in  the  oxides  of  zinc  or  mer- 
cury. 

“ But  by  combustion,”  the  boy  went  on,  “ many 


278 


THE  WONDERS  OF  SCIENCE. 


solid  bodies  are  converted  into  gases ; and  in  such 
cases,  according  to  Lavoisier’s  theory,  instead  of  heat 
being  evolved,  it  should  be  absorbed , and  positive 
cold  produced  by  the  process  of  burning. 

“ This,  however,  is  not  the  case,”  added  Humphry. 
“ The  explosion  of  Gunpowder , for  example,  is  at- 
tended by  immense  heat,  and  yet  the  ingredients 
composing  it,  in  passing  from  the  solid  to  the  gas- 
eous state,  expand  some  hundred-fold,  having  their 
volume  increased,  it  is  said,  no  less  than  250  times. 

So,  again,  the  gas  called  Protoxide  of  Chlorine , at 

• 

the  instant  of  decomposition  evolves  light  and  heat 
with  explosive  violence,  and  yet  it  is  known  to  be- 
come one-fifth  greater  in  volume  afterwards.  The 
oily  substance,  too,  called  Chloride  of  Nitrogen , on 
being  made  to  enter  into  combustion,  is  resolved 
into  its  elements  with  tremendous  force  of  inflam- 
mation, expanding  into  more  than  600  times  its 
bulk : so  that,  according  to  Lavoisier’s  theory,  a pro- 
digious degree  of  cold  ought  to  be  produced  by  such 
an  expansion,  whereas  light  and  heat  are  evolved 
by  it.” 

That  the  heat  of  combustion  is  due  rather  to  in- 
tense chemical  action  going  on  at  such  times,  Hum- 
phry made  many  experiments  to  prove. 

First,  he  generated  some  Chlorine , or  green  gas.* 

* Chlorine  gas  was  called  “ oxy-muriatic  acid ” when  Davy  was 
a boy,  from  being  supposed  to  be  a compound  of  oxygen  and  muri- 
atic acid  gas.  Davy,  however,  afterwards  proved  that  this  same 


THE  WONDERFUL  EFFECTS  OF  HEAT.  279 

This  he  did  by  mixing  in  a retort  some  common 
salt  with  a little  black  oxide  manganese,  and  some 
sulphuric  acid  and  water.  The  gas  which  came  over 
was  of  a greenish-yellow  colour,  and  had  a pun- 
gent, disagreeable  smell,  exciting  cough  and  great 
irritation  in  the  lungs  when  inhaled.  Having  col- 
lected some  of  this  gas  over  warm  water  in  a re- 
ceiver, with  a stop-cock  at  the  top,  the  boy  took 
a retort  which  had  another  stop-cock  fitted  to  the 
end  of  it,  and  having  introduced  into  this  some  cop- 
per-leaf, he  screwed  the  retort  on  to  the  plate  of 
his  air-pump,  and  proceeded  to  exhaust  it  of  air  as 
perfectly  as  he  could.  This  done,  he  screwed  the 
stop-cock  of  the  retort  on  to  that  of  the  receiver  in 
which  he  had  collected  the  gas ; then,  turning  on 
both  cocks,  the  chlorine  rushed  up  into  the  retort, 
and  the  metal  immediately  became  spontaneously 
ignited  by  it,  and  burnt  in  the  gas  with  considerable 
energy. 

The  experiment  was  then  repeated  with  a little 
powdered  antimony,  and  the  same  vivid  combustion 
ensued. 

Now  these  Humphry  knew  to  be  cases  of  mere 
chemical  affinity . The  chlorine  gas  had  a strong 
tendency  to  combine  with  the  metals  employed,  and 
as  these  were  used  in  the  best  form  for  promoting 

oxy-muriatic  acid  contained  no  oxygen  whatever,  and  was  rather 
an  elementary  substance,  being  incapable  of  being  resolved  into 
any  two  other  bodies. 


280 


THE  WONDERS  OF  SCIENCE. 


the  combination,  the  union  of  the  gas  with  the  cop- 
per and.  antimony  was  so  rapid  and  energetic,  that 
combustion  was  the  consequence.* 

Next,  the  lad  took  some  Sulphur , and  in  this  he 
heated  some  shavings  of  iron  in  a close  vessel,  wdien 
the  metal,  in  a short  time,  was  seen  to  become  in- 
tensely ignited,  and  to  burn,  as  it  were,  in  the  va- 
pour of  the  sulphur.  This  was  most  curious,  for 
sulphur  he  had  never  thought  to  be  a supporter  of 
combustion. 

F urther,  Humphry  heated  some  platinum  and  tin- 
foil,  and  at  the  moment  when  the  two  metals  fused 
into  one  mass  they  became,  to  his  astonishment,  viv- 
idly ignited. 

Nor  was  this  all : the  boy  slacked  some  recently- 
burnt  lime  in  a dark  place,  and  found  that,  when 
the  water  was  thrown  upon  it,  the  heat  rose  to  up- 
wards of  500°,  while  a faint  light  was  emitted. 

Another  substance,  discovered  since  the  date  of 
the  above  experiments,  affords  a striking  illustra- 
tion of  the  heat  produced  by  energetic  chemical  ac- 
tion. This  is  a peculiar  liquid  called  Peroxide  of 
Hydrogen  (see  p.  264),  consisting  merely  of  water 
combined  with  an  extra  quantity  of  oxygen.  So 
readily  decomposible  is  this  fluid,  that  at  the  heat  of 
boiling  water  evolutions  of  gas  are  produced  with 

* A piece  of  blotting-paper  dipped  in  oil  of  turpentine,  and 
introduced  into  a jar  of  chlorine  gas,  immediately  becomes  in-  ' 
flamed. 


THE  WONDERFUL  EFFECTS  OF  HEAT. 


281 


such  violence  as  to  cause  an  explosion ; and  almost 
all  the  metals,  when  in  a state  of  minute  division, 
resolve  it  rapidly  into  its  elements.  The  peroxides 
of  lead,  mercury,  gold,  platinum,  &c.,  act  on  the 
liquid  with  surprising  energy,  the  decomposition  of 
it  being  complete  and  instantaneous  upon  dropping 
those  substances  into  the  liquid;  for  oxygen  gas  is 
then  given  off  with  such  force  as  to  produce  a deto- 
nation, while  the  temperature  becomes  so  intense 
that  the  glass  tube  in  which  the  experiment  is  con- 
ducted grows  suddenly  red  hot. 

Subsequently,  Humphry  amused  himself  by  mix- 
ing a little  Chlorate  of  Potash , about  the  size  of  a 
pea,  with  the  same  quantity  of  loaf  sugar , having 
previously  reduced  each  to  powder.  Then  he  placed 
the  mixture  on  a piece  of  tile,  and,  dipping  a glass 
rod  into  a bottle  of  strong  Oil  of  Vitriol , let  the  acid 
drop  from  the  rod  upon  the  powdered  Chlorate  and 
sugar,  when  they  were  instantly  kindled,  and  burnt 
with  a red  and  blue  flame.  For  the  Vitriol  imme- 
diately decomposed  the  Chlorate  of  Potash,  and  so 
produced  heat  enough  to  ignite  the  materials  ; while 
the  oxygen  given  out  from  the  Chlorate  maintained 
the  sugar  in  a state  of  vivid  combustion.  A little 
Camphor , mixed  with  Chlorate  of  Potash , and  touch- 
ed with  a drop  of  Oil  of  Vitriol , may  be  made  to  in- 
flame in  the  same  manner.  A like  effect  is  also 
produced  when  the  Chlorate  is  mixed  with  Spirits  of 
Wine. 


2S2 


THE  WONDERS  OF  SCIENCE. 


After  this,  the  lad  placed  a small  piece  of  Phos- 
phorus, and  a few  grains  of  Chlorate  of  Potash , at 
the  bottom  of  a thin  glass  vessel,  and  then  poured 
gently  upon  them  some  hot  water.  The  heat  of 
the  water  was  sufficient  to  inflame  the  Phosphorus, 
while  the  oxygen  evolved  from  the  Chlorate  of  Pot- 
ash in  connexion  with  it  tended  to  keep  up  the 
combustion ; so  that  the  two  burnt  with  a vivid 
and  pleasing  light  under  the  water. 

Now  Humphry  knew  that  the  reason  of  these  ef- 
fects was,  that  the  Chlorate  of  Potash  contains  a 
large  quantity  of  oxygen,  which,  having  a strong 
tendency  to  combine  with  the  combustibles,  enters 
rapidly  and  energetically  into  union  with  them  im- 
mediately their  temperatures  are  elevated,  and  so 
gives  rise  to  the  phenomena  of  heat  and  light  which 
are  evolved  during  the  combustion. 

The  same  result  is  produced  by  Nitre  in  ordina- 
ry gunpowder,  for  this  also  contains  a large  quanti- 
ty of  oxygen  gas,  which  serves  to  inflame  the  small 
particles  of  charcoal  that  are  mixed  with  it,  while 
the  sulphur — which  forms  the  other  ingredient  — 
being  inflammable  at  a low  temperature,  renders 
the  gunpowder  capable  of  being  united  by  a mere 
spark. 

Oxygen  thus  appeared  to  Humphry  to  be  the  main 
“ supporter  of  combustion,”  while  the  body  burnt 
seemed  to  be  the  u combustible.” 

But  Humphry  had  seen  that  bodies  burnt  in 


THE  WONDERFUL  EFFECTS  OF  HEAT.  283 

Chlorine  gas  as  well  as  in  oxygen : this,  therefore, 
was  another  “supporter  of  combustion.”  The  same 
effect,  again,  he  had  found  to  be  produced  in  the  va- 
pour of  sulphur.  Sulphur,  however,  was  a “ combus- 
tible body so  that,  in  this  instance,  the  same  sub- 
stance was  both  a combustible  and  a supporter  of 
combustion. 

The  division  of  all  bodies,  therefore,  into  these 
two  classes,  as  propounded  by  the  French  chemists, 
appeared  to  have  no  foundation  in  nature. 

Nevertheless,  Humphry  was  determined  to  put 
the  matter  to  the  test  of  experiment,  and  to  see 
whether  the  light  and  heat  evolved  during  combus- 
tion proceeded  from  the  combustible  itself,  or  from 
the  combination  of  it  with  the  air  during  the  burn- 
ing. 

Accordingly,  the  lad  inflamed  a jet  of  hydrogen 
gas  in  a vessel  of  oxygen,  when  the  light  and  heat 
certainly  appeared  to  proceed  from  the  jet  of  hydro- 
gen, while  the  oxygen  seemed  to  act  merely  as  the 
supporter  of  the  combustion. 

On  reversing  the  experiment,  however,  and  caus- 
ing the  oxygen  gas  to  issue  from  the  jet,  Humphry 
found  that  he  could  inflame  it  in  a vessel  of  hydro- 
gen, and  that  then  the  light  and  heat  seemed  to  be 
evolved  from  the  burning  oxygen , while  the  hydro- 
gen appeared  only  to  keep  it  inflamed. 

It  was  evident,  therefore,  from  the  last  experi- 
ment, that  even  oxygen  itself  might  be  ranked 


284 


THE  WONDERS  OF  SCIENCE. 


among  the  combustibles , and  hydrogen  be  considered 
as  a supporter  of  combustion ; but  Humphry  now  saw 
that  the  real  truth  of  the  matter  was,  that  the  heat 
and  light  evolved  during  combustion  came  from  nei- 
ther one  substance  nor  the  other , but  arose  simply  from 
the  rapid  and  energetic  chemical  union  of  the  two  : 
for  even  two  metals,  at  the  moment  of  their  union, 
evolve  heat  and  light,  as  shown  in  the  experiment 
of  the  fusion  of  platinum  with  tin-foil. 

Combustion,  therefore,  is  simply  the  consequence 
of  the  rapid  chemical  action  of  one  body  upon  an- 
other ; and  the  reason  why  it  is  necessary  to  elevate 
the  temperatures  of  certain  bodies  before  they  can 
be  inflamed,  is  merely  because  heat  promotes  the 
chemical  action  of  substances  upon  each  other. 


CHAPTER  XI. 


HUMPHRY  AND  HIS  “ WONDERFUL  LAMP.” 

Humphry  found  it  impossible  to  quit  the  subject 
of  Combustion  without  some  inquiry  as  to  the  nature 
of  flame. 

“ What,”  said  he  to  himself,  “ are  those  brilliant 
sheets  of  light  that  dart  from  burning  substances'? 
And  why  is  it  that  certain  bodies  burn  with  the  ev- 
olution of  flame,  and  that  others  are  merely  capa- 
ble of  being  rendered  incandescent  at  the  highest 
heat  V’ 

Now  the  boy  had  before  reflected  upon  the  pro- 
duction of  heat  by  the  slow  combination  of  oxygen 
with  certain  combustible  substances,  so  he  immedi- 
ately passed  to  the  consideration  of  the  production 
of  light  by  the  same  means. 

He  knew  well  that  a stick  of  phosphorus  always 
appears  luminous  in  the  dark,  and  that  lines  of  fire 
can  be  written  with  it  on  a wall : the  reason  of  this 
being  simply  that  the  air  combines  with  it  slow- 


286 


THE  WONDERS  OF  SCIENCE. 


ly  at  ordinary  temperatures.  Again,  the  lad  was 
aware  that  decayed  wood  emits  a faint  light,  which 
is  visible  by  night,  the  light  being  due  to  the  same 
cause,  viz.  the  slow  combustion  which  is  continually 
going  on  in  it ; for  chemists  have  discovered  that 
the  rotting  vegetable  substance  is  constantly  absorb- 
ing oxygen  from  the  atmosphere,  and  evolving  car- 
bonic acid  gas — the  same  as  if  it  were  really  burn- 
ing— though  at  a less  rapid  rate.  Moreover,  the  de- 
cay of  many  animal  substances,  Humphry  had  read, 
is  attended  with  like  phenomena* — the  flesh  of  many 
fresh  and  saltwater  fish  becoming  luminous  previous 
to  putrefaction. 

But,  in  all  such  cases,  the  light  emitted  is  more 
like  a halo,  or  feeble  glow , than  the  character  of 
flame ; or,  rather,  it  seems  as  if  the  substance  had 
become  incandescent  in  the  cold , and  acquired  the  prop- 
erty of  ignition  at  ordinary  temperatures,  so  that  it 
was  capable  of  giving  out  light  without  being  sensi- 
bly heated.* 

Humphry  had  noticed,  too,  that  a green  wax  ta- 
per— the  colour  of  which  he  knew  to  be  produced 


* A few  flowers  have  also  the  property  of  emitting  light  at  or- 
dinary temperatures.  Among  these  may  be  cited  the  tube-rose , 
nasturtium , and  marigold , which  occasionally  give  out  flashes 
of  light  on  a warm  summer’s  evening.  This,  probably,  arises 
from  the  combination  of  the  oxygen  of  the  atmosphere  with 
the  vapour  of  the  volatile  oils  upon  which  the  perfumes  of  flow- 
ers are  known  to  depend.  Again,  other  substances  emit  light 
during  the  act  of  crystallization.  This  phenomenon  is  most  dis- 


HUMPHRY  AND  HIS  “WONDERFUL  LAMP.”  287 

by  “verdigris”  (acetate  of  copper) — on  being  light- 
ed and  blown  out  shortly  afterwards,  will  continue 
glowing  in  the  wick,  or  burning  without  flame,  until 
the  whole  of  the  taper  be  consumed. 

Now  this,  the  boy  was  well  aware,  was  another 
case  of  combustion,  going  on  at  a temperature  below 
that  of  flame,  though  it  was  a state  of  continuous 
incandescence,  requiring  a higher  heat  for  its  pro- 
duction than  the  phosphorescence  of  decaying  vege- 
table and  animal  matter. 

Having  thought  the  matter  well  over  for  some 
little  time,  the  boy-Chemist  eventually  conceived 
that  it  might  be  possible,  by  some  such  means,  to 
produce  a lamp  which  would  burn  continuously, 
and  give  light,  without  flame  ; and  this  he  imagined 
might  be  found  of  great  service  in  the  coal-mines, 
since  the  fire-damp  was  not  explosible  at  the  high- 
est red  heat , and  required  positive  flame  to  cause  it 
to  enter  into  combustion. 

In  the  case  of  the  glowing  wick  of  a green 
taper,  the  youth  saw  that  it  was  necessary  for  the 
wick  itself  to  be  made  red  hot  before  the  ignition 


tirictly  observed  during  the  gradual  deposit  of  arsenious  acid, 
when  dissolved  in  hot  hydrochloric  acid  (spirits  of  salts).  In  a 
dark  place  each  crystal,  as  it  is  formed,  may  be  seen  to  emit  a 
spark  of  light ; and  on  shaking  the  flask,  so  many  crystals  are 
sometimes  suddenly  produced,  that  vivid  flashes  become  percep- 
tible. The  cause  of  this  phenomenon  is  probably  dependent  on 
the  fixation  of  oxygen  by  the  arsenic  at  the  moment  of  precipi- 
tation. 


288 


THE  WONDERS  OE  SCIENCE. 


could  be  maintained ; and  he  concluded  that  it 
was  merely  the  incandescence  of  the  wick  which 
caused  the  gases  given  off  from  the  taper  to  com- 
bine with  the  air,  and  so  to  keep  it  continually  red 
hot.  It  struck  him,  therefore,  that  if  he  were  to  use 
some  combustible  liquid  that  was  highly  vaporisa- 
ble,  like  ether,  and  to  suspend  above  this  a spiral 
coil  of  fine  platinum  wire,  which  had  been  previ- 
ously heated  to  redness,  the  same  continuous  state 
of  ignition  might  be  made  to  go  on,  and  that  in  a 
much  simpler  manner. 

Accordingly,  Humphry  procured  a tall  ale-glass, 
and  having  poured  into  it  a tea-spoonful  of  ether, 
he  suspended  within  it  a coil  of  plati- 
num-wire, which  had  been  made  red 
hot  in  the  flame  of  a spirit-lamp. 

The  arrangement  of  the  little  appa- 
ratus is  represented  in  the  annexed  en- 
graving. 

Immediately  the  red-hot  coil  was 
placed  in  the  vapour  from  the  liquid,  the  excited 
boy  was  overjoyed  to  see  it  glow  with  a bright  red 
heat.  He  stood  watching  it  for  a long  time,  and 
was  rejoiced  to  find  that  there  was  not  the  least 
diminution  of  the  incandescence  till  the  whole  of 
the  liquid  had  disappeared,  and  the  vapour  been 
made  by  the  heat  of  the  wire  to  combine  with  the 
surrounding  air. 

Still  it  struck  Humphry  that  a more  convenient 


HUMPHRY’S  FIRST  ATTEMPT  AT  THE  SAFETY  LAMP.— Page  291. 


HUMPHRY  AND  HIS  “ WONDERFUL  LAMP.”  291 

mode  of  attaining  the  same  end  might  be  devised ; 
so  he  took  an  ordinary  spirit-lamp  (for  spirits  of 
wine  he  was  aware  had  the  same  tendency  to  give 
off  vapour  as  the  liquid  he  had  previously  em- 
ployed), and  wound  a coil  of 
fine  platinum  wire  round  the 
wick  — thus.  Then,  having 
lighted  the  lamp,  he  suffered  it 
to  burn  a few  seconds,  after 
which  he  put  an  extinguisher 
over  the  flame,  and  instantane- 
ously removed  it.  The  conse- 
quence was,  that  the  coil  retained  heat  enough  to 
carry  on  the  sloiv  combustion  of  the  vapour  from  the 
spirit,  so  that  the  ignition  was  kept  up,  and  the 
wire  continued  glowing,  till  the  whole  of  the  spirit 
had  evaporated  from  the  lamp. 

Overjoyed  at  the  discovery  he  had  made,  Hum- 
phry hastened  to  exhibit  his  lamp  without  a flame 
to  Mr.  Borlase  and  Mrs.  Foxell,  and  his  old  friend 
Mr.  Tonkin  : and  as  he  did  so,  the  boy  descanted 
fervently  upon  the  superiority  of  such  a means  of 
obtaining;  light  in  coal-mines  over  the  u steel-mills  ” 
which  were  then  used  for  the  purpose. 

Mrs.  Foxell  was  as  pleased  as  the  boy  himself  at 
what  she  considered  the  successful  termination  of 
his  labours ; and  when  Humphry  ran  over  to  her 
the  long  train  of  investigation  he  had  pursued  in 
order  to  arrive  at  the  object,  she  was  warm  in  her 


292 


THE  WONDERS  OF  SCIENCE. 


praises  of  his  perseverance  and  genius,  and  assured 
him  that,  by  such  patient  inquiry,  he  must  ulti- 
mately gain  the  honours  and  the  universal  esteem 
which  he  so  much  desired. 

Mr.  Borlase  was  surprised  at  the  talent  of  his 
young  pupil,  and  went  with  him  to  Mr.  Tonkin  to 
talk  over  the  matter ; and  when  Humphry’s  foster- 
father  saw  what  he  had  achieved,  and  was  informed 
of  the  benevolent  spirit  which  had  stirred  him  to 
the  discovery,  the  old  gentleman  hugged  the  lad  to 
him,  and  told  him  he  was  well  repaid  for  all  the  care 
and  affection  he  had  bestowed  upon  him. 

When,  however,  the  first  impressions  had  sub- 
sided, and  Humphry’s  exultation  at  the  discovery 
he  had  made  had  been  toned  down  by  continually 
reflecting  upon  the  subject,  he  began  to  think  his 
little  safety -lamp  might  be  much  improved  if  he 
could  only  increase  the  light  from  it.  In  its  pres- 
ent form  he  thought  it  would  be  available  merely 
in  such  cases  as  the  steel-mill  was  used,  viz.  to  ex- 
plore those  mines  which  were  known  to  be  charged 
with  fire-damp.  The  miners,  nevertheless,  needed 
some  light  at  their  work,  and  if  candles  or  lanterns 
were  employed,  the  flame  would  be  sure  to  ignite 
any  fire-damp  that  might  accidentally  become  mixed 
with  the  atmosphere,  and  so  to  cause  the  whole  to 
explode. 

What  was  required,  therefore,  was  a light  which 


HUMPHRY  AND  HIS  “ WONDERFUL  LAMP.”  293 

would  be  as  bright  as  those  the  miners  employed  at 
their  work,  but  which  would,  at  the  same  time,  be 
incapable  of  inflaming  the  explosive  gases  evolved 
from  the  coals. 

Such  a light  Humphry  knew  could  be  obtained 
only  from  flame  itself,  for  he  was  now  satisfied  that 
it  was  impossible  for  any  one  to  see  to  work  by  the 
rays  from  a red-hot  wire.  Still  the  difficulty  was, 
that  the  presence  of  flame  would  be  sure  to  cause 
the  fire-damp  to  explode  whenever  it  became  mixed 
with  the  air  in  the  mines,  and  it  was  impossible  to 
make  a lamp  burn  without  air. 

For  a time  the  difficulties  involved  in  the  con- 
struction of  such  a lamp  appeared  to  the  lad  to 
be  insurmountable.  At  length,  however,  nothing 
daunted,  he  set  to  work  to  discover  the  nature  of 
flame  itself,  and  so  to  find  out  what  conditions 
wrere  necessary  for  the  production  and  maintenance 
of  it. 

“ Flame”  said  Humphry,  while  reflecting  upon 
the  subject,  “ may  be  regarded  merely  as  a sheet , 
or  film,  of  gas,  in  a high  state  of  ignition.  The  tem- 
perature of  flame  is  always  very  intense,  since  it  will 
ignite  substances  that  cannot  be  lighted,  even  with 
the  highest  heat  of  incandescence.  The  light , how- 
ever, emitted  by  different  flames  is  by  no  means 
equally  vivid,  since  there  are  gases  which  burn  with 
the  production  of  a flame  so  feeble  as  to  be  scarcely 
visible  in  broad  daylight.” 


294 


THE  WONDERS  OF  SCIENCE. 


Accordingly  it  struck  the  boy,  that  the  best  way 
to  proceed  would  be  to  produce  a feeble  light  first, 
and  then  to  ascertain  by  what  means  he  could  in- 
crease the  brilliance  of  it.  So  Humphry  made  a 
large  bladder  full  of  hydrogen  gas,  and  then  another 
bladder  of  oxygen,  and  proceeded  to  burn  the  gases 
together  by  means  of  two  blow-pipes. 

The  flame  produced  was  of  a very  faint  blue  col- 
our, and  though  the  boy  closed  the  shutters,  he 
could  barely  see  to  read  by  the  light,  and  yet  the 
heat  of  it  was  almost  as  intense  as  any  that  could 
be  artificially  generated  ;*  for,  on  holding  a pla- 
tinum wire  in  the  flame,  it  immediately  became 
white  hot,  and  the  light  was  considerably  aug- 
mented. 

“ So,  then,”  cried  Humphry,  “ the  light  emitted 
by  a flame  seems  to  be  increased  by  solid  substances 
introduced  into  it,  and  ignited  by  it.” 

This  set  the  boy  wondering  what  would  be  the 
effect  if  he  were  to  cause  some  fine  dust  to  pass  con- 
tinually through  the  flame,  and  whether  the  bright- 
ness of  the  light  would  be  as  much  increased  then 
as  it  was  when  the  platinum  wire  was  introduced 
into  it. 

The  idea  had  no  sooner  struck  him  than  he  ran 
down  to  the  shop,  and  procuring  a little  magnesia 

* The  blue  colour  of  the  oxy-hydrogen  flame  is  due,  probably, 
to  the  particles  of  water  formed  by  the  combustion  of  the  two 
gases. 


HUMPHRY  AND  IHS  “WONDERFUL  LAMP.”  295 

in  fine  powder,  proceeded  to  sift  this  into  the  flame 
produced  by  the  oxygen  and  hydrogen  gases. 

The  result  was  almost  magical. 

No  sooner  did  the  fine  white  particles  fall  into 
the  flame,  than  the  light  was  changed  from  a faint 
blue  into  a brilliant  white ; while  the  little  solid 
specks  shone  like  so  many  gem-points  in  the  sun- 
shine, producing  a glare  that  it  pained  the  eyes  to 
look  at,  and  that  instantly  lighted  up  the  little  dark 
chamber  almost  with  the  vividness  of  daylight. 

“It  is  as  I expected!”  shouted  Humphry,  as  he 
gazed  with  admiration  at  the  beautiful  white  light ; 
“ the  luminosity  of  a flame  depends  chiefly  upon 
the  particles  of  solid  matter  diffused  through  it,  and 
rendered  incandescent  by  the  burning  gases.  The 
flame  of  a candle  or  oil-lamp,”  the  boy  continued, 
“ owes  its  brightness  merely  to  the  same  cause  ; for 
there  the  oil,  or  grease,  is  converted  into  gas  by  the 
heat  of  the  wick,  and  this  gas  consists  chiefly  of 
carburetted  hydrogen — that  is  to  say,  of  charcoal 
and  hydrogen  combined  together:  so  that  in  burn- 
ing, the  hydrogen  unites  with  the  oxygen  of  the  air 
and  forms  water,  while  the  charcoal  is  set  free,  and 
passes  up  through  the  flame  in  the  form  of  very 
minute  particles,  which  being  burnt  there,  and  so 
rendered  nearly  white  hot,  cause  the  light  to  shine 
with  great  vividness.” 

To  prove  that  the  light  of  an  ordinary  candle,  or 
oil-lamp,  is  due  merely  to  the  brilliancy  of  the  in- 


296 


THE  WONDERS  OF  SCIENCE. 


candescent  particles  of  charcoal  continually  passing 
through  the  flame,  the  lad  was  not  satisfied  merely 
with  holding  a burning  candle  against  the  ceiling, 
and  so  causing  the  unburnt  charcoal  to  be  deposited 
upon  it  in  the  form  of  u lamp-black,”  as  it  is  called  ; 
but  he  passed  some  hydrogen  gas  through  a small 
reservoir  of  naphtha,  and  found  that  the  brilliancy 
of  the  light  was  greatly  increased  by  it : for,  the 
naphtha  being  merely  a liquid  form  of  charcoal  and 
hydrogen  in  combination,  the  gas,  on  traversing  the 
fluid,  took  up  a certain  portion  of  the  naphtha  in 
vapour,  and  this  being  very  rich  in  charcoal,  was 
the  cause  of  the  increased  illuminating  power  given 
to  the  flame. 

The  same  principle  has  been  applied  since  Hum- 
phry’s time  to  the  production  of  some  of  the  most 
vivid  of  our  artificial  lights.  The  “ Drummond 
light,”  for  instance — which  consists  merely  of  a jet 
of  oxygen  and  hydrogen  gases  projected  against 
a cylinder  of  lime — owes  its  intense  brilliancy 
solely  to  the  particles  of  lime  that  are  rendered 
white  hot  by  the  flame  of  the  burning  gases ; and 
that  the  lime  passes  oflf  in  vapour  is  proved  by  the 
fact,  that,  during  the  combustion,  the  roof  of  the 
lantern  becomes  covered  with  the  sublimed  parti- 
cles. 

Again,  the  brilliancy  of  the  electric  light  itself  is 
known  to  arise  from  the  particles  of  white-hot 
charcoal  that  pass  over  in  vapour  from  one  pole 


HUMPHRY  AND  HIS  “WONDERFUL  LAMP.”  297 

of  the  battery  to  the  other;  for  it  is  found  that 
the  charcoal  point  in  connexion  with  the  positive 
pole  becomes  decreased  and  burnt  into  a cavity, 
while  that  in  connexion  with  the  negative  pole  is 
proportionately  increased,  having  a small  knob 
or  protuberance  of  charcoal  deposited  upon  it: 
so  that,  strange  as  it  may  appear,  the  brilliancy 
of  the  flame  of  a common  tallow-candle  depends 
upon  the  same  cause  as  that  of  the  electric  light 
itself.  In  the  one  case,  however,  the  combustion 
being  imperfect,  the  points  of' charcoal  are  less 
vividly  ignited ; whereas  in  the  other,  the  heat 
being  the  most  intense  that  can  be  produced  by 
artificial  means,  the  incandescence  is  proportion- 
ately higher,  and  the  brilliancy  of  the  light,  there- 
fore, increased  to  the  greatest  point.  In  a word, 
the  particles  of  charcoal  in  the  flame  of  a candle 
are  only  at  an  orange  heat,  whereas  those  in  the 
voltaic  flame  are  at  the  highest  white  heat  that  art 
can  generate. 

Accordingly,  artificial  light  would  appear  to  be 
due  solely  to  artificial  heat,  and  the  illuminating 
power  of  even  flame  itself  to  depend  upon  the  in- 
candescence of  the  particles  of  solid  matter  diffused 
through  the  burning  gases. 

Humphry’s  next  object  was  to  discover  whether 
flame  really  consisted,  as  he  before  said,  of  a sheet 
or  film  of  gas  in  a state  of  combustion. 


298 


THE  WONDERS  OF  SCIENCE. 


u The  flame  of  a common  candle,”  lie  mused, 
u appears  to  be  a solid  cone  of  luminous  matter.  Is 
it,  however,  really  alight  in  the  middle?”  the  boy 
mentally  inquired ; “ or  is  it  burning  at  the  outside 
only,  so  that  the  thin  film  of  white-hot  vapour  in- 
closes a portion  of  combustible  matter  within  it, 
which  cannot  burn  for  want  of  air?  How  can  I 
ascertain  this?” 

Humphry  thought  for  a while,  and  then  it  struck 
him,  that  if  he  were  to  place  a piece  of  thin  glass 
upon  the  flame  itself,  so  as  to  press  it  down  as  it 
were,  he  could  then  see  whether  or  not  it  were 
alight  in  the  middle;  for  if  it  were  alight  round 
the  edge  only,  he  would  behold  through  the  glass  a 
bright  ring  of  flame,  with  a dark  spot  in  the  centre, 
indicating  the  portion  where  the  combustion  was  not 
going  on. 

The  experiment  was  soon  tried,  and  the  result 
proved  as  Humphry  had  anticipated.  A luminous 
circle  was  seen  through  the  glass,  at  the  point 
where  the  flame  touched  the  surface,  and  in  the 
centre  of  this  there  was  a dark 

7 

/ spot,  like  a black  wafer,  showing 
where  the  decomposed  charcoal 
gas  existed  in  the  interior  of  the 
flame  in  an  unburnt  state.  The 
appearance,  however,  is  represent- 
ed in  the  subjoined  illustration. 
Indeed  Humphry  perceived,  that  as  air  was  neces- 


HUMPHRY  AND  HIS  “WONDERFUL  LAMP.”  299 


sary  for  combustion,  and  it  was  impossible  for  the 
atmosphere  to  get  to  the  interior  of  the  flame,  the 
outside  only  of  the  cone  of  combustible  gases,  evolved 
from  the  decomposed  tallow,  could  be  alight ; while 
the  vapour  in  the  centre  could  be  burnt  merely  as 
it  passed  off  into  the  air  at  the  upper  part  of  the 
flame. 


The  next  step  was  to  see  whether  the  interior 
dark  part  of  the  flame  really  consisted  of  the  same 
inflammable  gases  as  were  in  a state  of  combustion 
at  the  exterior,  or  surface  of  it. 

Accordingly,  Humphry  placed  a small  glass  tube 
within  the  centre  of  the  flame 
from  an  ordinary  candle,  and  found 
that  the  unburnt  gas  from  the  in- 
terior readily  made  its  way  up 
the  tube,  and  escaped  at  the  top 
of  it,  and  that  on  applying  a light 
to  this  it  was  immediately  ignited ; 
so  that  two  flames  were  thus  pro- 
duced from  one  candle,  as  here 
shown. 

Another  proof  that  the  gases  in  the  interior  of 
the  flame  were  not  in  a state  of  combustion  was 
afforded  by  lighting  some  spirits  of  wine  in  a large 
spoon ; for  Humphry  then  found  that  he  could 
introduce  some  grains  of  gunpowder,  and  even 
some  pieces  of  phosphorus,  by  means  of  a tube, 


300 


THE  WONDERS  OF  SCIENCE. 


into  the  middle  of  the  flame,  without  igniting 
them. 

Humphry,  moreover,  could  now  see  that  the  rea- 
son why  the  blow-pipe  so  much  increased  the  heat 
of  an  ordinary  flame  is  simply  because  a current  of 
air  is  made  by  such  means  to  traverse  the  interior 
part  of  it,  so  that  the  combustion  being  rendered 
more  perfect,  the  temperature,  of  course,  becomes 
proportionately  higher. 

Again,  the  wick  of  the  “Argand  Lamp”  is  con- 
structed circular,  so  that  a current  of  air  may  be 
supplied  to  the  interior  of  the  flame  ; and  hence  the 
superior  brilliancy  of  this  kind  of  burner.  Table- 
lamps  are  now  generally  made  upon  the  same  prin- 
ciple, and  so,  indeed,  are  the  gas-burners  in  shops. 
Sometimes,  however,  a jet  is  used,  with  the  holes  so 
arranged  as  to  spread  the  gas  into  a thin  wide  sheet, 
and  thus  allow  the  air  to  act  upon  a large  surface 
of  combustible  matter  at  each  side.  These  are  called 
u bat's  wing ” and  “fish-tail”  burners,  &c.,  according 
to  the  shape  of  the  flat  broad  flames  produced  by 
them. 

The  next  point  in  the  inquiry  was  to  discover 
what  would  be  the  effect  of  cooling  down  a flame, 
since  it  was  evident  that  it  required  a very  high  tem- 
perature for  its  existence. 

Humphry  was  well  aware  that,  by  projecting  a 
current  of  cold  air  upon  substances  in  a state  of 


HUMPHRY  AND  HIS  “WONDERFUL  LAMP.”  301 


combustion,  the  flames  were  generally  extinguished. 
Still  lie  wished  to  see  whether  it  Was  not  possible 
to  lower  the  temperature  of  a flame  by  some  other 
means. 

Accordingly  he  procured  a piece  of  wax-candle, 
and  proceeded  to  pull  out  all  the  wick,  except  one 
thread,  so  that  when  it  was  lighted  the  flame  from  it 
should  be  as  small  as  possible.  Then  the  boy  made 
a little  ring  of  iron  wire,  about  the  eighth  of  an  inch 
in  diameter,  and  this  he  affixed  to  a wooden  handle. 
Passing  the  wire  rfcig  over  the  lighted  wick  he  found, 
that  on  bringing  it  a little  below  the  flame  the  light 
was  immediately  extinguished,  for  the  metal,  being 
a good  conductor  of  caloric,  served  to  carry  oft’  the 
heat  which  was  necessary  for  the  maintenance  of  the 
flame. 

It  then  struck  Humphry  that  the  pins  which 
housewives  stuck  in  rushlights  that  they  wished  to 
be  extinguished  at  a certain  time,  acted  merely  upon 
the  same  principle — the  metal  carrying  oft*  the  heat, 
and  so  lowering  the  temperature  requisite  for  the  ex- 
istence of  the  light. 

The  youth  thought  for  a long  time  as  to  whether 
he  could  avail  himself  of  this  principle  in  any  way 
for  the  construction  of  his  safety-lamp,  for,  as  he 
had  now  discovered  that  it  was  possible  to  extin- 
guish flame  merely  by  reducing  its  temperature — 
and  that  a piece  of  wire,  placed  in  connexion  with 
it,  did  this  most  effectually — he  fancied  he  might 


302 


THE  WONDERS  OF  SCIENCE. 


take  advantage  of  some  such  means  for  preventing 
the  passage  of  flame  to  fire-damp.  But  though  he 
racked  his  brain  long  he  could  hit  upon  no  plan  for 
accomplishing  his  object.  So  he  contented  himself 
with  merely  making  a memorandum  of  the  fact  in 
his  note-book,  saying  to  himself,  that  he  knew  it 
would  prove  serviceable  some  day — and  then  passed 
on  to  another  part  of  his  inquiry. 

Fire-damp,  he  was  well  aware,  is  explosible  only 
when  mixed  with  the  atmosphere ; for  the  air  is 
necessary  for  the  combustion  of  all  substances,  and 
explosion,  as  before  observed,  is  merely  the  result 
of  instantaneous  combustion . Still,  certain  liquids, 
Humphry  knew,  are  attracted  by  the  sides  of  fine 
tubes,  so  that  the  fluid  in  which  they  are  immersed 
is  maintained  within  them  above  the  level  of  that 
without.  He  knew,  too,  that  by  the  same  princi- 
ple a certain  quantity  of  water  might  be  retained 
in  a fine  sieve  without  running  through  the  holes ; 
and  that  a vessel  full  of  small  holes  might,  for 
the  like  reason,  be  immersed  to  a certain  depth  in 
water  without  sinking,  or  any  of  the  liquid  enter- 
ing it. 

So  the  lad  was  anxious  to  see  what  would  be  the 
effect  of  fine  tubes  upon  gases,  and  whether,  upon 
passing  an  explosive  mixture  of  carburetted  hydro- 
gen and  air  along  a narrow  glass  pipe,  the  flame 
would  pass  down  it,  or  be  arrested  in  its  progress. 

Accordingly,  having  prepared  some  carburetted 


HUMPHRY  AND  HIS  “WONDERFUL  LAMP.”  303 

hydrogen  gas,  and  mixed  it  with  eight  parts  of  air 
— for  these  proportions  he  had  found  to  be  the  most 
explosive — he  passed  the  mixture  along  a glass  tube, 
the  bore  of  which  was  only  -t-th  of  an  inch  in  diame- 
ter, and  discovered,  on  lighting  the  gas  that  issued 
from  the  end  of  it,  that  the  flame,  instead  of  travel- 
ling down  the  narrow  channel,  and  being  instantly 
communicated  to  the  whole  of  the  explosive  mix- 
ture, remained  stationary  at  the  orifice  of  the  tube, 
where  the  gases  burnt  as  slowly  and  quietly  as  with 
an  ordinary  candle. 

Humphry  was  half-bewildered  with  joy  at  the  dis- 
covery he  had  made.  Fire-damp  he  had  now  ascer- 
tained was  not  explosible  within  narrow  tubes,  and 
instantly  a hundred  and  one  plans  flashed  across  his 
mind  for  rendering  the  fact  serviceable  to  those  en- 
gaged in  the  coal-mines. 

Still  there  was  much  to  work  out.  It  was  nec- 
essary to  know  through  how  large  a tube  flame  was 
capable  of  being  transmitted  ; so  he  procured  another 
glass  pipe,  the  bore  of  which  was  a quarter  of  an  inch 
in  diameter,  or  double  that  of  the  one  he  had  first 
employed,  and  passing  the  same  explosive  mixture 
along  it,  he  found  that,  on  lighting  the  gases  at  the 
end  of  this,  the  flame  no  longer  remained  stationa- 
ry at  the  orifice,  but  travelled  slowly  down  the  chan- 
nel, taking  more  than  a second  before  it  reached  the 
other  end,  though  the  tube  itself  was  only  a foot 
long. 


304 


THE  WONDERS  OF  SCIENCE. 


Then  pursuing  the  same  course  of  experiments, 
Humphry  subsequently  discovered  that  by  diminish- 
ing the  diameter  of  the  tube  he  could  shorten  the 
length  of  it  without  any  danger  of  the  flame  travel- 
ling along  it,  and  so  causing  the  ga^es  without  to  ex- 
plode. Moreover,  the  lad  ascertained  that  when  fine 
metal  tubes  were  substituted  for  glass  ones,  the  secu- 
rity was  even  more  perfect. 

To  insure  greater  safety,  however,  by  making  the 
channel  through  which  the  explosive  gases  passed  as 
fine  as  possible,  he  ultimately  inserted  some  short 
pieces  of  metal  tubing,  one  within  the  other ; so 

that  the  bores  being  of  dif- 
ferent diameters,  they  formed 
a series  of  broad  concentric 
rings,  each  enclosing  anoth- 
er, and  having  a fine  channel 
between  them — thus. 

These  Humphry  proved  to 
be  perfectly  secure  against  all 
explosion,  and  then  proceeded  to  fix  one  set  at  the 
bottom  of  a lamp,  and  another  at  the  top  of  a glass 
chimney  that  was  made  to  fit  air-tight  round  the 
flame.  The  concentric  tubes  at  the  bottom  were  for 
the  supply  of  air  to  the  light,  and  those  at  the  top  for 
the  issue  of  the  smoke ; so  that  thus,  if  any  fire- 
damp were  present  in  the  mine,  and  entered  with 
the  atmosphere  through  the  air-tubes  at  the  bottom, 
the  flame  would  not  be  communicated  to  the  explo- 


HUMPHRY  AND  HIS  “ WONDERFUL  LAMP.”  305 


sive  gases  outside  the  lamp — and  thus  the  safety  of 
the  miner  would  be  thoroughly  ensured. 

For  rendering  the  arrangement  adopted  more  in- 
telligible, a design  of  Davy’s  first  Safety-Lamp  is 
here  given. 

The  principle  upon  which  this 
lamp  depended  for  its  security 
had  been  so  carefully  worked  out 
that  it  scarcely  required  testing. 

To  assure  himself,  however,  of 
its  efficacy,  the  boy  immersed  the 
lamp  in  the  most  explosive  mix- 
ture of  carburetted  hydrogen  and 
air  that  he  could  possibly  form, 
and  was  well  repaid  for  all  his 
labours  by  seeing  that  the  flame 
was  incapable  of  being  trans- 
mitted to  the  combustible  gases 
without;  so  that,  upon  their  entering  the  lamp, 
the  light  itself  was  extinguished.  In  a word,  he 
found  that  his  lamp  was  “absolutely  safe,”  and 
that  the  fire-damp  had  been  disarmed  by  him  of 
its  terrors. 

Humphry’s  friends  were  as  delighted  as  the  boy 
himself  at  the  successful  termination  of  his  labours. 
Mrs.  Foxell,  who  had,  in  the  first  instance,  encour- 
aged him  to  proceed,  was,  perhaps,  the  most  grati- 
fied of  all ; nor  did  she  refrain  from  lecturing  her 
brother,  Mr.  Borlase,  upon  his  previous  want  of 


U 


306 


THE  WONDERS  OF  SCIENCE, 


faith  in  the  accomplishment  of  the  result,  telling 
him  that  it  was  cruel,  where  so  many  lives  were 
at  stake,  to  damp  the  ardour  of  any  one  who  could 
believe  in  the  possibility  of  rendering  them  secure 
for  the  future. 

Mr.  Borlase  was  sufficiently  generous  to  confess 
his  error,  and  frankly  acknowledged  that  he  never 
thought  Humphry  -would  be  able  to  accomplish  half 
as  much  as  he  had. 

The  boy’s  old  friend,  Mr.  Tonkin,  too,  felt  proud- 
er than  ever  of  his  foster-son,  when  he  saw  the  lad 
test  the  powers  of  the  lamp  in  his  presence ; and 
the  old  gentleman  made  Humphry’s  heart  swell 
again  with  the  praises  he  heaped  upon  him,  and  the 
tears  start  to  his  eyes  with  the  confession  of  the 
long  love  he  had  borne  the  boy. 

At  length,  however,  Mr.  Tonkin  said  that  he 
thought  one  improvement  still  was  required,  though 
how  it  was  to  be  effected  he  must  leave  Humphry 
to  find  out,  for  it  was  more  than  he  could  manage. 
On  the  admission  of  the  fire-damp  into  the  lamp 
the  light  was  extinguished.  u This,”  the  old  gen- 
tleman observed,  “ appeared  to  be  a great  defect, 
for  the  extinction  of  the  flame  was  a sure  indica- 
tion that  danger  surrounded  those  who  carried  the 
lamp ; and  to  leave  the  miner  in  darkness  at  a time 
when  immediate  flight  was  necessary,  struck  him  as 
being  a serious  drawback  to  its  utility.  If  Hum- 
phry, therefore,”  he  said,  u could,  by  some  means 


HUMPHRY  AND  HIS  “WONDERFUL  LAMP.”  307 

or  other,  arrange  it  so  that  the  light  should  con- 
tinue burning,  even  in  the  presence  of  the  fire-damp 
itself,  the  ingenuity  of  the  apparatus  would  not  only 
be  much  greater,  but  its  value  be  considerably  en- 
hanced.” 

Humphry  saw  the  force  of  Mr.  Tonkin’s  objec- 
tion, and  it  struck  him  that  the  defect  was  almost 
irremediable.  He  was,  therefore,  not  a little  vex- 
ed to  find  that  an  instrument  which  he  had  fancied 
perfect,  was  not  altogether  faultless. 

The  lad  pondered  over  the  matter  for  many  days, 
and  tried  a number  of  experiments  to  overcome  the 
difficulty  which  had  been  raised.  It  proved,  how- 
ever, beyond  his  powers ; so,  exhausted  by  his  long 
study,  and  vexed  at  the  idea  of  his  comparative  fail- 
ure, Humphry,  at  length,  dismissed  the  subject  from 
his  mind,  and  locked  the  safety -lamp  in  his  cupboard, 
determined  that  it  never  should  be  made  public  un- 
til it  was  perfect  in  all  its  arrangements. 

It  was  in  vain  that  Mrs.  Foxell  urged  him  to 
make  known  the  invention,  even  in  an  unfinished 
state  ; but  the  boy  was  firm  in  his  resolve.  “ Some 
day,”  said  he,  “it  shall  be  completed,  and  then  the 
world  may  have  it,  and  welcome ; but  as  it  is  now, 
it  is  hardly  worth  either  the  giving  or  accepting,  and 
no  honours  can  come  of  it.  When  I know  more,” 
he  added,  “ I can  do  better  : nor  do  I intend,  be- 
cause I have  been  baffled  in  this  my  first  project, 
to  give  over  studying ; for  I find  such  delight  in 


808 


THE  WONDERS  OF  SCIENCE, 


the  perception  of  the  new  truths  which  are  daily 
unfolded  to  me,  that  I would  rather  forego  any 
source  of  pleasure  than  that  which  comes  from  sci- 
entific discovery,” 

It  was  many  years  before  the  Safety-Lamp  was 
perfected ; and  when  it  was,  the  alteration  was  so 
slight,  that  it  has  been  well  observed — “The  his- 
tory of  this  elaborate  inquiry  affords  a striking  proof 
of  the  inability  of  the  human  mind  to  apprehend 
simplicities  without  a long  process  of  previous  com- 
plication.”* 

Humphry  Davy,  as  we  have  narrated,  had  al- 
ready discovered,  while  experimenting  upon  the  in- 
flaming of  explosive  gases  in  narrow  tubes,  that, 
provided  he  diminished  the  bore,  he  could  shorten 
the  length  of  them  in  a corresponding  ratio.  Now 
a sheet  of  wire-gauze,  it  is  obvious,  consists  merely 
of  a series  of  fine  tubes,  of  very  short  lengths.  It 
appears  strange,  therefore,  that  our  hero  was  some 
time  before  he  conceived  the  happy  idea  of  con- 
structing his  lamp  entirely  of  wire-gauze,  instead 
of  feeding  it  with  air  through  narrow  channels,  or 
“safety  canals,”  as  he  called  them;  for,  as  flame 
cannot  be  transmitted  along  small  tubes,  it  is  man- 
ifest that,  on  surrounding  a lamp  with  a wire-gauze 
cylinder,  or  cage,  the  fire-damp,  as  it  enters  with 
the  air,  will  burn  within  the  cage  itself,  and  the 
* Dr.  Paris’s  “ Life  of  Sir  Humphry  Davy.”  p.  352. 


HUMPHRY  AND  HIS  “WONDERFUL  LAMP.”  309 

flame  be  incapable  of  passing  through  the  small  ap- 
ertures in  the  gauze,  and  thus  exploding  the  gas 
outside  of  it. 

To  render  the  action  of  wire-gauze  in  this  respect 
more  intelligible,  a few  of  Humphry  Davy’s  after- 
experiments may  be  cited  in  connexion  with  this 
part  of  the  subject. 

If  a small  piece  of  wire-gauze  (say  about  9 inches 
square,  and  having  about  30  meshes  to  the  square 
inch)  be  gradually  brought  down  upon  the  flame 
of  a candle,  the  flame  itself  will  be  cut  off  where  it 
touches  the  gauze,  and  merely  a dark  spot  be  there 
observed,  encircled  by  a ring  of  light,  while  the 
combustible  matter  of  the  flame  will  issue  through 
the  small  apertures  in  the  form  of  smoke ; for  dur- 
ing the  passage  of  the  burning  gases  through  the 
metallic  meshes  they  will  be  so  far  cooled  down 
that  the  flame  will  be  extinguished,  and  thus  ren- 
dered incapable  of  traversing  the  gauze  itself. 

If,  however,  a lighted  taper  be  held  above  the 
wire-gauze,  the  inflammable  gas  or  smoke  from  the 
candle  will  be  immediately  rekindled,  and  the  flame 
continue  to  burn  then,  both  on  the  upper  and  under 
side  of  the  tissue. 

But  the  impermeability  of  metallic  gauze  to  flame 
may  be  rendered  still  more  evident,  by  placing  a 
piece  of  fine  wire  web  above  a jet  of  gas  previous 
to  lighting  it,  when  it  will  be  found  that,  if  a burn- 
ing taper  be  held  over  the  wire  web,  the  gas  will 


310 


THE  WONDERS  OF  SCIENCE. 


be  kindled  above  it,  and  continue  to  burn  ^ipon  the 
gauze  itself,  while  the  combustible 
matter  beneath  will  remain  unig- 
nited; for  the  metallic  threads, 
being  good  conductors  of  heat, 
will  so  cool  the  dame  as  to  pre- 
vent it  passing  through  to  the  gas 
on  the  lower  side. 

Again,  if  a small  piece  of  cam- 
phor be  laid  in  the  centre  of  a sheet  of  wire-gauze, 
and  a light  held  beneath  it,  the  vapour  from  the 
camphor,  which  is  very  inflammable, 
will  be  made  to  burn  with  a bright 
flame  downwards  — instead  of  up- 
wards, as  flames  usually  do — while 
the  camphor  itself  will  lie  upon  the  upper  side  of  the 
tissue  in  an  uninflamed  state. 

The  power  of  metallic  webbing  thus  to  inter- 
cept or  extinguish  flame,  depends  simply  upon  the 
cooling  effect  it  produces;  so  that  as  flame  requires 
a high  temperature  for  its  existence,  it  is  plain 
that  it  no  sooner  becomes  cooled,  by  being  passed 
through  a good  conductor  of  heat,  than  it  is  extin- 
guished. 

If,  however,  the  meshes  of  the  wire-gauzp  be 
not  sufficiently  small,  or  if  the  wire  of  the  gauze 
itself  becomes  intensely  heated,  the  flame  will  tra- 
verse it  in  either  instance;  because  the  cooling 

power  is  reduced,  in  the  one  case,  by  the  largeness 


HUMPHRY  AND  HIS  “WONDERFUL  LAMP.”  311 

of  the  apertures,  and  in  the  other  by  the  high  tem- 
perature of  the  wire. 

For  the  knowledge  of  these  facts,  we  repeat,  we 
are  indebted  to  the  after-investigations  of  Davy  him- 
self. 

Now  it  is  evident  from  the  above  experiments, 
that  if  a lamp  be  covered  with  a cylindrical  cage 
of  wire-gauze,  no  flame  will  be  able  to  pass  from  the 
interior  of  the  lamp  to  the  exterior  of  it,  in  conse- 
quence of  the  cooling  power  of  the  metallic  web  en- 
compassing it;  so  that,  if  the  surrounding  air  be 
charged  with  an  explosive  gas,  it  will  enter  the  lamp 
through  the  meshes  of  the  web  and  burn  within  the 
cage,  while  that  without  will  remain  unkindled. 

Such,  then,  is  the  principle  of  the  “ Safe-Lamp” 
as  perfected  by  Davy,  and  which  is  here  shown : 


312 


THE  WONDERS  OF  SCIENCE. 


The  safety  of  this  lamp  may  be  exhibited  by  im- 
mersing it  in  a large  jar,  at  the  bottom  of  which  is 
a little  Ether ; for  the  vapour  from  this  liquid,  on 
mingling  with  the  air,  forms  a highly  inflammable 
atmosphere.  On  introducing  the  lamp  into  this, 
the  flame  first  becomes  enlarged  and  is  then  extin- 
guished, while  the  whole  of  the  cage  remains  filled 
with  a lambent  blue  light.  On  withdrawing  the 
lamp,  however,  and  bringing  it  into  the  open  air, 
the  wick  is  suddenly  rekindled,  and  the  flame  re- 
turns to  its  natural  size  and  colour. 

For  perfect  safety,  it  is  necessary  that  the  wire- 
gauze  of  these  lamps  should  contain  about  30  wires, 
or  900  apertures  in  every  square  inch,  and  that  the 
heat  of  the  wire  itself  should  never  rise  above  red- 
ness; for  “if,”  as  Davy  said,  “the  iron  wire  be- 
come white  hot,  the  lamp  will  be  no  longer  safe. 
This,  however,”  he  adds,  “ need  never  happen  in  a 
colliery ; for  if  a workman  finds  the  temperature  of 
the  wire  increasing  rapidly  in  an  explosive  atmos- 
phere, he  can  easily  diminish  the  heat  by  turning 
his  back  upon  the  current,  and  keeping  it  from  play- 
ing upon  the  gauze  by  means  of  his  clothes.” 

Of  this  wonderful  lamp  it  has  been  well  said, 
“that  it  is  a present  from  Philosophy  to  the  Arts, 
and  to  the  class  of  men  farthest  removed  from  the 
interests  of  science.  We  know  of  no  discovery  in 
which  the  admirer  of  Science  and  the  lover  of  man- 
kind have  greater  reason  to  congratulate  one  an- 


HUMPHRY  AND  HIS  “ WONDERFUL  LAMP.”  313 

other.  The  discovery,”  adds  the  late  Professor  Play- 
fair, “is  in  no  degree  the  effect  of  accident;  and 
chance,  which  comes  in  for  so  large  a share  in  the 
credit  of  human  inventions,  has  no  claims  on  this, 
which  is  altogether  the  result  of  patient  and  enlight- 
ened research.  The  great  use  of  an  immediate  and 
constant  appeal  to  experiment  cannot  be  better 
evinced  than  in  this  example.  The  result  is  as 
wonderful  as  it  is  important.  An  invisible  and  im- 
palpable barrier,  made  effectual  against  a force  the 
most  violent  and  irresistible  in  its  operations,  and  a 
power  that,  in  its  tremendous  effects,  seemed  to 
emulate  the  lightning  and  the  earthquake,  confined 
within  a narrow  space,  and  shut  up  in  a net  of  the 
most  slender  texture ; these  are  facts  which  must 
excite  a degree  of  wonder  and  astonishment,  from 
which  neither  ignorance  nor  wisdom  can  defend  the 
beholder.  When  to  this  we  add  the  beneficial  con- 
sequences, and  the  saving  of  the  lives  of  men,  and 
consider  that  the  effects  are  to  remain  as  long  as 
coal  continues  to  be  dug  from  the  bowels  of  the 
earth,  it  may  fairly  be  said  that  there  is  hardly,  in 
the  whole  compass  of  art  or  science,  a single  inven- 
tion of  which  one  would  rather  wish  to  be  the  au- 
thor.”* 

It  should  be  borne  in  mind,  moreover,  that  Davy 
in  the  accomplishment  of  his  noble  task,  nqt  only 
did  not  seek,  but  positively  rejected  all  pecuniary  re- 

* “Edinburgh  Review,”  January,  1816 


314 


THE  WONDERS  OF  SCIENCE. 


ward ; so  that  it  becomes  difficult  which  to  admire 
the  most — the  benevolence  which  prompted  him  to 
undertake  the  long  train  of  laborious  investigations, 
the  genius  which  carried  him  to  so  .successful  an 
issue,  or  the  noble  disinterestedness  which  bade  him 
refuse  to  traffic  in  an  invention  that  was  destined  to 
mitigate  the  sufferings  of  some  of  the  poorest  and 
least  educated  of  his  fellow-creatures.* 

* “It  will  hereafter  be  scarcely  credited,”  says  Dr.  Paris, 
“ that  an  invention  so  eminently  philosophic,  and  which  could 
never  have  been  derived  but  from  the  sterling  treasury  of  science, 
should  have  been  claimed  in  behalf  of  an  enginewright  of  Killing- 
worth  colliery,  of  the  name  of  Stephenson  ; a personnot  even  pro- 
fessing a knowledge  of  the  elements  of  chemistry .”  The  “ engine- 
wright” here  sneered  at  for  his  ignorance,  ultimately  rose  to  be 
the  great  George  Stephenson,  the  inventor  of  the  locomotive. 
How  would  the  fashionable  physician  speak  of  the  quondam  en- 
ginewright of  Killingworth  colliery  now ! Stephenson’s  lamp 
was  formed  on  the  principle  of  admitting  the  fire-damp  by  nar- 
row tubes,  and  “in  such  small  detached  portions,  that  it  would 
be  consumed  by  combustion.”  The  two  lamps  were,  doubtless- 
ly, distinct  inventions,  though  Davy,  in  all  justice,  appears  to  be 
entitled  to  precedence — not  only  in  point  of  date,  but  as  regards 
the  long  chain  of  inductive  reasoning  concerning  the  nature  of 
flame  by  which  his  result  was  arrived  at. 


CHAPTER  XII. 


HUMPHRY  PRACTISES  AS  A SURGEON ON  HIMSELF. 

Humphry  by  this  time  desired  some  little  recrea- 
tion. He  had  been  at  work  for  many  weeks  unin- 
terruptedly— his  days  given  to  his  profession,  and 
his  leisure,  in  the  evenings,  devoted  to  the  pros- 
ecution of  his  scientific  discoveries ; and  what  with 
the  exhaustion  of  continuous  thought,  and  the  vexa- 
tion at  his  inability  to  perfect  the  lamp,  from  which 
lie  had  such  high  hopes  of  honour,  the  lad  felt  in- 
competent to  resume  his  labours  until  his  mind,  by 
diversion,  had  recovered  somewhat  of  its  ordinary 
elasticity. 

Accordingly,  he  determined  upon  enjoying  a day 
or  two’s  fishing  with  his  uncle  Millett — for  this  was 
Humphry’s  favourite  pastime  throughout  life;  and 
the  sport,  his  biographer  tells  us,  “ was  alike  his  re- 
lief in  toil  and  his  solace  in  sorrow.”* 

* “ Davy’s  passion  for  angling  betrayed  itself  upon  all  occa- 
sions,” says  Dr.  Paris  ; “whenever  I had  the  honour  of  dining 
at  his  table,  the  conversation,  however  it  might  have  commenced, 


316 


THE  WONDERS  OF  SCIENCE. 


It  was  now  spring,  moreover,  when  the  small 
streams,  the  youth  knew,  were  in  the  best  state 
for  angling — turbid,  in  a slight  degree,  from  the 
mild  rains  common  in  April  and  May ; so  Hum- 
phry, having  arranged  his  tackle  on  the  over-night, 
sallied  forth  the  next  morning  to  join  his  uncle  at 
Marazion. 

The  lad’s  fishing  costume  was  singular  enough  to 
claim  some  notice.  It  consisted  of  an  entire  suit 
of  green — that  colour  being  considered  by  him  the 
most  likely  to  elude  the  observation  of  the  fish. 
The  coat  was  half  covered  with  lappets  of  the 
many  pockets  for  holding  the  necessary  tackle ; 
and  his  hat  (which  was  a round  felt  one,  with  a 
broad  brim  like  a wagoner’s),  had  been  dyed  of 
the  same  colour  as  his  clothes  by  a pigment  of  his 
own  composition ; while  round  the  hemispherical 
crown  were  coiled  a series  of  fine  lines,  each  term- 

invariably  ended  on  fishing  ; and  when  a brother  of  the  angle  hap- 
pened to  be  present,  you  had  the  pleasure  of  hearing  all  his  en- 
counters with  the  finny  tribe — how  he  had  lured  them  by  his 
treachery,  and  vanquished  them  by  his  perseverance.  He  would 
occasionally  strike  into  a most  eloquent  and  impassioned  strain 
upon  some  subject  which  warmed  his  fancy  ; such,  for  example, 
as  the  beauties  of  mountain  scenery  : but  before  you  could  fully 
enjoy  the  prospect  which  his  imagination  had  pictured,  down  he 
carried  you  into  some  sparkling  stream,  or  rapid  current,  to  floun- 
der for  the  next  half-hour  with  a hooked  salmon.  . . . Nothing 
irritated  him  so  much  as  to  find  that  his  companions  had  caught 
more  fish  than  himself,  and  if,  during  conversation,  a brother  fish- 
erman surpassed  him  in  the  relation  of  his  success,  he  betrayed 
similar  impatience,’' 


✓ 


HUMPHRY  EQUIPPED  FOR  A FISHING  EXCURSION.— Page  319. 


HUMPHRY  PRACTISES  ON  HIMSELF. 


319 


mating  in  some  peculiarly-coloured  artificial  fly : 
so  that  the  hat  appeared  somewhat  like  a clod  of 
turf  upon  which  so  many  bees  and  moths  had  set- 
tled. His  legs,  again,  were  encased  in  a huge  pair 
of  jack-boots,  which,  for  the  convenience  of  wading 
through  the  water,  reached  above  his  knees ; in- 
deed, as  Macbeth  says  of  the  witches,  “ He  looked 
not  like  an  inhabitant  o’  the  earth,  and  yet  was 
on  t.  ‘ 

Thus  equipped,  Humphry,  as  we  said,  sallied 
forth,  with  the  joints  of  his  rod  strapped  together 
— like  a small  bundle  of  fagots — and  resting  on  his 
shoulder,  while  at  his  back  projected  the  wicker  fish- 
basket,  as  if  it  were  a huge  cartouche-box.  Over 
the  other  shoulder  were  slung  the  heavy  jack-boots, 
and  at  his  side  ambled  his  favourite  water-spaniel 
“ Chloe,”  her  long  tail  wagging  as  she  stopped  now 
and  then  to  look  up  in  her  master’s  face,  for  she 
seemed  to  be  as  delighted  as  the  boy  himself  at  the 
anticipation  of  the  sport  that  she  knew  was  about 
to  ensue. 

The  youth  paused  occasionally  to  fondle  the 
knowing  creature,  for  he  had  her  since  a pup — 
having  begged  the  gift  of  her  when  she  was  taken 
from  her  mother,  and  about  to  be  drowned  with  the 
rest  of  the  litter  as  soon  as  born,  and  it  was  only  by 
great  care  that  he  had  been  able  to  rear  her,  so  that 

* See  Dr.  Paris’s  description  of  Davy’s  ordinary  fishing  cos- 
tume, p.  189, 


320 


THE  WONDERS  OF  SCIENCE, 


the  two  were  as  attached  to  each  other  as  any  hu- 
man friends  could  be ; nor  did  Humphry  treat  her 
as  a dumb  animal,  but  spoke  to  her  as  though  she 
understood  every  word  he  said : and,  perhaps,  in  his 
heart,  the  boy  (with  his  half-poetic  and  half-meta- 
physic  theories)  believed,  she  did.*' 

It  was  late  that  evening  before  the  couple  return- 
ed from  the  day’s  sport,  and  then  Cliloe  carried  in 
her  mouth  a small  basket  containing  a portion  of 
the  spoil,  for  Humphry’s  wicker  knapsack  was  not 
capacious  enough  for  the  whole,  as  he  and  his  uncle 
Millett  — so  runs  the  record  — had  caught  no  less 
than  “ seven  dozen  trout  in  the  rivulet  and  mill- 
pond near  the  residence  of  the  Rev.  Mr.  Giddy,  in 
the  parish  of  St.  Earth.” 

Humphry’s  success  at  his  sport  had  made  him 
too  light-hearted  to  feel  the  fatigues  of  the  day,  and 
although  he  was  somewhat  foot-sore  from  the  long 
use  of  the  heavy  boots  he  now  carried  over  his 
shoulder,  the  boy  and  Cliloe  jogged  merrily  past  the 
tanneries  at  the  extreme  west  of  the  town ; for  the 
dog  knew  as  well  as  her  master,  by  the  leathery 

* “This  favourite  dog  is  well  remembered  in  Penzance, ” 
says  Davy’s  brother.  “ My  sister  writes,”  he  adds,  “that  ‘on 
his  first  return  from  Bristol,  after  an  absence  of  about  twelve 
months,  Chloe  did  not  remember  him,  till  he  called  her  by  name, 
and  then  she  was  in  a transport  of  joy.’  Her  descendants  are 
now  numerous  in  the  Mount’s  Bay,  and  prized  for  good  quali- 
ties ” Yol.  i.  p.  54. 


HUMPHRY  PRACTISES  ON  HIMSELF. 


321 


smell  that  filled  the  air  at  that  quarter,  that  they 
were  not  far  from  home  then ; and  Humphry,  as  he 
patted  the  fond  animal,  promised  her  a good  supper 
of  fish  for  all  that  she  had  done  that  day. 

As  they  passed  down  Market-Jew  Street  the  oil- 
lamps  and  candles  were  being  lighted  in  some  of  the 
little  shops,  and  Humphry  saw,  as  he  looked  towards 
the  Town-Hall  at  the  end  of  the  street,  that  the  sun 
had  long  since  set,  for  the  sky  was  grey  with  the 
thickening  dusk,  and  the  stars  were  beginning  to 
peep  out  of  the  haze,  one  after  another,  through  the 
darkening  firmament. 

At  length  the  Town-Hall  itself  was  reached,  and 
the  youth  was  telling  Chloe  that  she  should  soon 
have  her  supper  now,  when  suddenly  a loud  cry 
was  heard.  As  the  lad  turned  round  towards  the 
street  that  led  to  Madem  Church  to  ascertain  the 
cause  of  the  noise,  he  beheld  to  his  horror  a huge 
dog,  at  full  speed,  hurrying  in  that  direction,  white 
with  foam  at  the  mouth,  and  followed  by  a mob  of 
affrighted  people,  hooting  and  hallooing  at  its  heels. 
Some  of  the  men  were  armed  with  pikes,  and  oth- 
ers carried  muskets,  intent  on  the  destruction  of  the 
rabid  animal. 

Humphry,  with  Chloe  still  by  his  side,  was  within 
a few  paces  of  the  furious  creature.  The  boy  saw  in 
an  instant  that  flight  was  impossible,  and  dreading 
lest  his  favourite  dog  should  be  attacked,  he  shouted 

X 


322 


THE  WONDERS  OF  SCIENCE. 


“Back!  back!”  to  her  in  his  most  commanding 
tone.  The  order,  however,  was  too  late,  for  Chloe, 
being  a little  in  advance  of  her  master,  had  already 
attracted  the  notice  of  the  infuriated  brute,  and 
Humphry  saw  her  danger  at  a glance.  In  another 
moment  his  own  dog  would  be  seized  by  the  rabid 
one,  and  the  slightest  graze  from  its  teeth  he  knew 
would  be  sufficient  to  render  Chloe’ s immediate  de- 
struction a matter  of  duty.  It  was  no  time  for  re- 
flection, so  the  excited  boy,  eager  to  save  the  life  of 
his  favourite  spaniel,  rushed  past  her  with  his  heavy 
fishing-rod  raised  high  in  the  air,  and  ready  to  fell 
the  dangerous  brute  to  the  earth. 

Ere  he  could  aim  a blow,  however,  the  hunted 
dog  had  fastened  on  Humphry’s  leg,  and  fixing  his 
fangs  in  the  flesh,  inflicted  a wound  that  made  the 
lad  shriek  again  with  the  suddenness  of  the  pain. 

The  cry  of  her  master  brought  Chloe  instantly 
to  the  rescue,  and  dropping  her  basket  of  fish  she 
sprang,  yelping,  towards  the  savage  brute.  Hum- 
phry knew  the  peril  of  the  encounter,  and  finding 
the  animal  about  to  relax  its  hold  of  his  flesh,  he 
seized  it  by  the  neck  and  held  its  head  firmly  to  the 
ground,  while  the  townsfolk  rushed  immediately  to 
the  spot,  and  with  their  weapons  soon  put  an  end  to 
all  the  danger. 

“Tha  bee’st  bitten,  Master  Humphry,”  shouted 
Malachy  Carteret,  as  he  drew  his  adze  from  the 


HUMPHRY  PRACTISES  ON  HIMSELF. 

head  of  the  animal;  “run  tha  to  Dr.  Borlase  di- 
rectly, and  ha’  the  bite  looked  to,  or  tha  life,  poor 
boy,  a’ n’t  worth  a dried  pilchard.” 

Then  came  Jan  Fenberthy  the  miller— as  white 
as  plaster-cast  in  his  working  dress — and  he,  with 
a cluster  of  others  behind,  were  anxious  in  their 
inquiries  as  to  what  was  the  nature  of  the  wound, 
while  each  had  some  novel  and  different  remedy  to 
recommend. 

Humphry,  however,  knew  sufficient  of  his  pro- 
fession to  be  aware  that  it  was  no  time  for  hesi- 
tation ; so,  while  the  eager  throng  crowded  around 
him,  he  raised  the  leg  of  his  trousers,  and  observing 
the  marks  of  the  animal’s  teeth  in  his  flesh,  he  de- 
liberately drew  liis  knife  from  his  pocket,  and  there, 
upon  the  spot,  cut  out  the  lacerated  part  without  a 
wince. 

This  striking  instance  of  the  boy’s  intrepidity 
was  hailed  with  wonder  by  the  people  about  him. 
and  one  and  all  were  loud  in  their  praises  of  his 
courage  and  decision.  Many  who  had  known  him 
from  a child  rushed  up  and  shook  him  warmly  by 
the  hand,  while  others,  who  had  been  the  com- 
panions of  his  father,  declared  he  was  Robert  Davy’s 
own  son  every  inch  of  him — indeed  all  there  had 
some  encouraging  word  to  say  or  some  kindness  to 
proffer. 

Humphry,  however,  was  too  sick  and  faint  from 
loss  of  blood  to  be  able  to  listen  to  the  remarks  of 


324  THE  WONDERS  OF  SCIENCE. 

those  about  him ; so,  having  tied  his  handkerchief 
round  the  wound,  he  begged  Malachy  Carteret  to 
help  him  home  to  Dr.  Borlase’s.  And  as  the  lit- 
tle carpenter  curled  the  boy’s  arm  about  his  neck 
Humphry  limped  along  with  Chloe  at  his  side,  who 
kept  looking  up  sadly  in  his  face,  as  if  she  was 
aware  of  all  that  had  happened,  while  the  boy  ex- 
claimed as  he  went,  “ Thank  God  I have  saved  your 
life,  poor  Chloe,  even  though  it  be  at  the  expense  of 
my  own.” 

Following  in  the  wake  of  Humphry  and  Mal- 
achy walked  many  of  the  crowd  — one  carrying 
the  boy’s  fishing-rod,  another  his  jack-boots,  and 
another  the  basket  of  trout  that  Chloe  had  dropped 
in  the  road ; and  as  they  went  along,  they  won- 
dered among  themselves  whether  Master  Humphry 
would  get  the  better  of  the  bite ; and  some  told  cu- 
rious country  tales  as  to  how  the  poison  had  re- 
mained in  the  blood  for  years  afterwards,  so  that  a 
person’s  life  was  never  safe  from  it. 

On  reaching  the  surgery,  Humphry  found  that 
Mr.  Borlase  had  been  called  to  visit  a patient  in 
the  country  that  evening ; so,  being  left  to  his  own 
resources,  he  proceeded  forthwith  to  apply  some 
lunar  caustic  to  the  wound  himself,  and  having 
done  this,  he  begged  Mrs.  Foxell  (who  was  fright- 
ened to  tears  at  the  dangerous  accident  he  had 
met  with)  to  make  his  excuses  to  her  brother,  the 
doctor,  when  he  returned,  for  the  poor  bov  told  her 


HUMPHRY  PRACTISES  ON  HIMSELF. 


325 


lie  was  anxious  to  reach  his  mother’s  house  before 
the  news  of  his  having  been  bitten  by  a mad  dog 
was  carried  home,  so  that  he  might  lighten  her 
alarms  on  his  account. 

Humphry,  however,  had  barely  taken  leave  of 
Mrs.  Foxell  before  Mrs.  Davy  herself  rushed  into 
the  surgery,  half  frantic  with  fear  at  what  she  had 
heard ; and  she  no  sooner  caught  sight  of  him  than 
she  fell  upon  his  neck,  and  wept  and  laughed  by 
turns,  hysteric  with  the  intensity  of  her  emotion. 

The  boy  endeavoured  to  assuage  her,  assuring 
her  that  from  the  promptness  and  vigour  of  the 
remedies  he  had  applied  there  was  little  cause  for 
alarm.  But  to  no  avail : the  poor  woman  was 
satisfied  her  darling  boy  was  doomed  to  the  most 
frightful  of  all  deaths  sooner  or  later,  saying,  u that 
if  she  was  deprived  of  him  her  cup  of  bitterness 
would  be  full  indeed.”  Then  the  heavy  privations 
she  had  already  suffered  in  life  rose  again  to  her 
mind,  and  in  the  agony  of  her  despair  at  the  ca- 
lamity which  now  threatened  her  she  wrung  her 
hands,  and  cried  aloud  to  God  to  have  mercy  upon 
her. 

Nor  could  she  in  any  way  be  soothed  until  the 
lad  told  her  it  was  necessary  for  him  at  such  a time 
to  remain  in  perfect  quietude,  and  that  the  least  ex- 
citement might  develope  the  very  symptoms  which 
she  dreaded. 

This  had  the  desired  effect.  Such  was  her  love 


326 


THE  WONDERS  OF  SCIENCE. 


and  care  of  the  boy,  that  not  another  tear  did  she 
afterwards  shed  in  his  presence  ; but,  dismissing  her 
own  trials,  she  talked  to  him  only  of  the  subjects 
she  knew  he  delighted  in ; and,  when  she  had  him 
removed  to  her  own  house,  she  sat  by  his  bed,  day 
after  day  and  night  after  night,  reading  to  him  from 
works  on  the  different  sciences  till  his  eyes  were 
closed  in  sleep,  and  then  the  poor  widow  would  fall 
upon  her  knees,  and  with  her  pent-up  tears  stream- 
ing  in  secret  from  her  eyes,  and  her  voice  choked 
with  her  sobs,  pray  the  Great  Ruler  of  All  to  spare 
the  only  protector  left  her. 


/ 


HUMPHRY'S  MOTHER  READING  TO  HIM  PUKING  HIS  ILLNESS.  — Page  826. 


/ 


' 


CHAPTER  XIII. 


THE  FIRST  SUN-PICTURES. 

Humphry  remained  confined  to  his  bed  for  many 
weeks,  and  every  day  his  mother  dreaded  seeing  some 
development  of  the  symptoms  which  generally  en- 
sue from  the  bite  of  so  rabid  an  animal ; but  the 
boy  assured  her,  again  and  again,  that,  owing  to  the 
promptitude  of  the  remedies  he  had  applied,  there 
was  no  cause  for  alarm. 

While  the  youth  was  still  a prisoner  in  his  room, 
a gentleman  came  to  lodge  at  the  house,  and  Hum- 
phry, to  his  great  delight,  learnt,  in  a few  days  aft- 
erwards, that  the  new  lodger  was  no  less  a person 
than  Mr.  Gregory  Watt,  son  of  the  celebrated 
James  Watt,  the  inventor  of  the  present  steam- 
engine. 

It  did  not  take  long  before  the  two  became  ac- 
quainted, and  then  Humphry  ascertained  that  the 
young  Mr.  Watt  had  but  recently  quitted  the  Uni- 
versity of  Glasgow,  and  had  been  recommended  by 


330 


THE  WONDERS  OF  SCIENCE. 


his  physicians,  owing  to  his  declining  state  of  health, 
to  reside  for  some  time  in  the  West  of  England; 
hence  the  cause  of  his  visit  to  Penzance. 

Nor  was  Humphry  long  in  discovering  that  the 
mind  of  his  new  friend  was  enriched  beyond  his  age 
with  science  and  literature,  and  that  he  possessed, 
like  himself,  a spirit  devoted  to  the  acquisition  of 
knowledge,  and  soaring  far  above  the  little  vanities 
and  distinctions  of  the  world.  The  two  kindred 
spirits,  therefore,  soon  contracted  an  intimacy  of  the 
warmest  nature ; and  this  ultimately  ripened  into  a 
friendship  which  continued  to  the  period  of  Mr. 
Watt’s  premature  dissolution. 

Mr.  Gregory  Watt  felt  not  a little  astonished, 
on  being  introduced  to  the  son  of  his  landlady, 
to  find  him  shortly  afterwards  speaking  upon  sub- 
jects of  metaphysics  and  poetry ; for  when  Mr. 
Watt  spoke  to  him  of  the  courage  he  had  displayed 
at  the  time  of  the  accident  in  excising  the  wound- 
ed parts  of  his  leg,  Humphry  confessed  “that  he 
had  no  belief  in  the  existence  of  pain,  whenever^ 
the  energies  of  the  mind  were  directed  to  counter- 
act it.”^'  “For,”  went  on  the  boy,  “in  states  of 
profound  attention,  all  perception  of  external  things 
fades  from  the  mind;  the  clock  in  the  room  ticks, 
and  we  hear  it  not ; persons  enter  the  apartment, 
and  their  presence  is  unheeded  by  us.  And  if 


* See  Dr!  Paris’s  “ Life  of  Davy,”  p.  12. 


THE  FIRST  SUN-PICTURES. 


331 


by  the  intensity  of  the  intellectual  operations  the 
senses  can  cease  performing  their  functions  in  the 
one  case,  why  not  in  the  other?  Martyrs  at  the 
stake  have,  while  in  deep  prayer,  held  their  hand 
unmoved  in  the  flames,  and  who  can  say  that  the 
very  fervour  of  their  heavenly  aspirations  did  not 
deprive  them  of  all  sense  of  pain  for  the  time  be- 
ing?” 

Mr.  Gregory  Watt,  however,  had  but  little  taste 
for  metaphysical  discussions ; and,  smiling  at  Hum- 
phry’s stoicism,  sought  to  divert  the  conversation 
into  a more  congenial  and  practical  channel. 

The  steam-engine  that  had  been  recently  set  up 
at  the  Wherry  Mine  by  Mr.  Watt’s  father  became 
the  theme  of  their  converse ; this  soon  led  to  com- 
ments on  the  theory  upon  which  its  powers  de- 
pended, and  then  Humphry’s  companion  was  sur- 
prised to  find  that  a youth,  who  had  been  brought 
up  in  an  obscure  town  in  Cornwall,  was  as  well 
acquainted  with  the  doctrine  of  “latent  heat” — 
and,  indeed,  the  whole  science  of  caloric  — as  he 
himself,  who  had  been  reared,  as  it  were,  in  a fac- 
tory, where  the  workings  of  it  were  every  day  visi- 
ble. 

The  new  laws  of  combustion  naturally  followed 
as  the  next  subject  of  discussion,  when  Humphry  ob- 
served, “ that  he  would  undertake  to  demolish  the 
French  theory  in  half-an-hour and  so  saying,  he 
rapidly  ran  over  the  experiments  he  had  performed, 


332 


THE  WONDERS  OF  SCIENCE. 


to  prove  the  falsity  of  Lavoisier’s  notions  respect- 
ing the  origin  of  heat  during  the  burning  of  sub- 
stances.^ 

The  lad  had  now  touched  the  true  chord,  and  the 
interest  of  Mr.  Watt  becoming  more  excited,  he  con- 
versed with  young  Davy  upon  his  chemical  pursuits, 
and  was  at  once  astonished  and  delighted  at  his  sa- 
gacity ; so  that  the  couple — congenial  in  taste — al- 
ready began  to  feel  a growing  friendship  for  each 
other. 

Humphry  had  quitted  his  chamber,  but  was  still 
confined  to  the  house,  from  his  inability  to  walk, 
when  Mr.  Watt  — who  had  now  known  the  youth 
long  enough  to  be  proud  of  his  acquaintance — re- 
turned from  his  morning’s  stroll  along  the  sea-shore, 
in  company  with  two  friends  whom  he  had  met  in 
the  town. 

The  gentlemen  proved  to  be  Mr.  Josiah  Wedg- 
wood, the  eminent  potter  of  Staffordshire,  and  his 
brother  Thomas,  who  was  alike  distinguished  for  his 
scientific  abilities. 

The  learned  potter  was  not  long  in  Humphry’s 
company  before  he  discovered  the  high  merits  of 
the  lad ; nor  was  he  a little  pleased  when  he  found 
that  the  young  Cornish  apothecary  knew  all  about 
the  pyrometer  he  had  invented  for  measuring  high 

* See  Dr.  Paris’s  account  of  Davy’s  first  interview  with  Greg- 
ory Watt.  p.  35. 


THE  FIRST  SUN-PICTURES. 


333 


degrees  of  heat  by  the  contraction  of  a ball  of 
clay;  and  the  old  gentleman  found  considerable 
delight  in  explaining  to  the  boy  the  various  pro- 
cesses concerned  in  the  manufacture  of  earthen- 
ware and  porcelain,  telling  him  anecdotes  as  to 
how  Bernard  Palissy  — who  was  the  first  to  dis- 
cover the  means  of  giving  a glaze  to  the  baked  clay 
— had  been  reduced  to  such  poverty  by  his  experi- 
ments, that  he  was  forced  to  burn  the  doors,  and 
even  the  boards,  of  the  house  in  which  he  lived, 
in  order  to  get  a supply  of  fuel  for  his  furnaces ; 
and  how  he  afterwards  amassed  an  immense  for- 
tune by  the  invention,  and  ultimately  died  in  the 
French  Bastille,  a martyr  to  the  Protestant  creed, 
which  he  had  espoused.  Mr.  Wedgwood  added  that, 
“When  we  eat  our  food  we  little  think  of  the  labour 
and  privations  that  have  been  endured  in  order  to 
give  a glassy  surface  to  the  plates  and  dishes  upon 
which  it  is  served ; for  but  few  are  aware  that,  pre- 
vious to  this  invention,  the  ordinary  earthenware 
articles  were  more  like  tiles  than  our  present  crock- 
ery.” 

Then  Mr.  Wedgwood  talked  with  the  youth 
about  the  rocks,  inquiring  whether  he  had  ever  no- 
ticed any  of  the  finer  species  of  clay  in  those  parts, 
and  was  surprised  to  find  how  closely  the  boy  had 
marked  the  changes  in  the  soil ; for  Humphry  told 
him  “ he  had  observed  that  the  felspar  in  the  gran- 


334 


THE  WONDERS  OF  SCIENCE. 


ite  decomposed  long  before  either  the  mica  or  the 
quartz,  and  that  it  was  chiefly  by  the  action  of  the 
atmosphere  upon  this  same  felspar  that  the  huge 
granite  rocks  became  disintegrated,  or  broken  up ; 
and  that,  as  the  felspar  consisted  principally  of  clay 
in  the  purest  form,  he  fancied  that  some  advantage 
might  be  taken  of  this  in  producing  a finer  species  of 
porcelain  than  had  yet  been  manufactured  in  this 
country.” 

The  old  gentleman  thanked  Humphry  for  his  sug- 
gestion, and  warmly  praised  him  for  his  observation 
and  sagacity ; whereupon  the  youth  promised,  imme- 
diately that  his  leg  would  permit  of  his  accompany- 
ing him,  to  point  out  to  Mr.  Wedgwood  the  places 
where  he  had  noticed  the  finest  deposits  of  felspar 
to  occur. 

The  conversation  then  changed  to  a subject  that 
Mr.  Josiah  Wedgwood  said  “he  had  no  doubt 
would  be  highly  interesting  to  one  of  Humphry’s 
turn  of  mind.”  The  old  gentleman  told  the  boy 
how  his  brother  Thomas  had  discovered  a means 
of  copying  pictures  upon  glass,  and  even  of  fixing 
the  images  of  the  camera  obscura , by  the  action  of 
light;  “ so  that,”  he  said,  “the  sun  itself  could  be 
made  to  turn  artist,  and  to  produce  a represent- 
ation of  an  object  that  no  human  hand  could  pos- 
sibly rival.” 

Humphry  was  enraptured  with  the  new  wonder, 


THE  FIRST  SUN-PICTURES.  335 

and  more  eager  than  ever  to  learn  all  about  it ; so 
he  begged  Mr.  Thomas  Wedgwood  to  explain  to 
him  the  whole  process. 

“ I should  tell  you,  then,”  said  the  potter’s  broth- 
er, “ that  it  has  been  long  known  to  chemists  that 
a solution  of  nitrate  of  silver  (called  lunar  caustic  in 
the  shops),  when  washed  over  a sheet  of  paper — al- 
though it  does  not  undergo  any  change  while  kept 
in  a dark  place — will  speedily  change  colour  on  be- 
ing exposed  to  daylight,  and  that  then  it  passes 
through  different  shades  of  grey  and  brown,  and  ul- 
timately becomes  nearly  black.  These  alterations 
in  colour,”  continued  Mr.  Thomas  Wedgwood,  “take 
place  more  rapidly  according  as  the  light  is  more  in- 
tense. In  the  direct  beams  of  the  sun,  two  or  three 
minutes  are  sufficient  to  cause  it  to  darken ; where- 
as in  the  shade,  several  hours  are  required  to  pro- 
duce the  full  effect.  The  light,  too,  when  trans- 
mitted through  different-coloured  glasses,  acts  upon 
the  nitrate  of  silver  with  different  degrees  of  intens- 
ity. It  is  found,  for  instance,  that  the  sunbeams, 
when  passed  through  red  or  yellow  glass  (so  that 
only  red  or  yellow  light  shall  fall  upon  the  paper), 
have  very  little  action  upon  the  lunar  caustic ; 
green  glass,  however,  is  more  efficacious,  while  blue 
and  violet  produce  the  most  decided  and  rapid 
changes. 

“Now  to  make  you  clearly  comprehend,”  went 
on  the  gentleman,  “the  reason  of  these  changes,  I 


336 


THE  WONDERS  OF  SCIENCE. 


should  tell  you  that  nitrate  of  silver  consists  of 
nitric  acid  (aquafortis)  and  silver,*  and  that  if  a 
vessel  of  pure  and-  colourless  nitric  acid  be  exposed 
to  the  sun’s  rays,  it  will  become  decomposed,  so 
that  red  fumes  of  nitrous  acid  will  be  evolved,  and 
these  mixing  partly  with  the  liquid  itself,  will  short- 
ly turn  it  to  a reddish-brown  tint.  Well,  the  same 
change  takes  place  when  the  nitric  acid  is  combined 
with  the  silver,  and  so  made  to  form  nitrate  of  sil- 
ver. The  consequence  is,  that  as  the  nitrous  acid 
which  is  evolved  is  unable  to  combine  directly  with 
the  silver,  the  decomposed  aquafortis  is  dissipated 
in  the  form  of  vapour,  while  the  silver  itself  re- 
mains behind  in  the  paper ; and  in  such  an  extreme 
state  of  minute  division,  that  the  particles,  instead 
of  being  white,  like  ordinary  silver,  appear  black  to 
our  eyes.” 

Humphry  expressed  himself  delighted  with  the  ex- 
planation, and  said  he  could  now  see  how  it  was  pos- 
sible to  produce  sun-pictures  by  such  means.  Still 
he  begged  Mr.  Wedgwood  to  proceed. 

That  gentleman  then  told  Humphry  that  his  first 
attempt  concerning  the  production  of  sun-pictures, 
was  to  fix  the  evanescent  images  formed  by  the 
camera  obscura,  but  though  he  was  able  to  impress 

* For  the  sake  of  simplicity,  the  nitric  acid  is  here  made  to 
consist  (according  to  the  new  theory)  of  N06+H  (instead  of 
N05+H0),  and  so  to  combine  directly  with  the  metal  as 
NOe  + Ag  (instead  of  with  the  oxide  as  N05+0Ag). 


THE  FIRST  SUN-PICTURES. 


337 


these  upon  paper  in  a bright  sunlight,  he  found 
that  he  could  not  produce  them  in  any  moderate 
time  in  ordinary  daylight ; so  that,  from  the  length 
of  time  required  before  the  impression  was  taken, 
the  effects  of  light  and  shade  had  materially  altered. 
“ With  paintings  on  glass,  however,”  he  added,  “ I 
have  been  more  successful ; in  order  to  copy  these 
I apply  the  solution  of  nitrate  of  silver  to  leather, 
for  this  I find  to  be  more  readily  acted  upon  than 
paper — probably  owing  to  the  tanning  in  the  ma- 
terial. When  the  surface  of  leather  is  thus  pre- 
pared, I place  it  behind  a painting  upon  glass,  and 
expose  it  to  the  solar  light,  when  the  rays,  being 
transmitted  through  the  different  parts  of  the  pic- 
ture, produce  distinct  gradations  of  black  and  white, 
according  to  the  lights  and  shades  in  the  original ; 
for  where  the  light  passes  freely  through  the  glass, 
the  colour  of  the  nitrate  of  silver,  of  course,  be- 
comes the  deepest.  By  this  means,  then,  you  will 
perceive  that  the  lights  and  shades  of  my  picture 
are  entirely  reversed  : all  the  black  parts  in  the  orig- 
inal being  left  white  in  the  copy,  since  the  light, 
being  unable  to  pass  through  these,  cannot  act  upon 
the  solution ; while  all  the  white  parts  of  the  orig- 
inal, on  the  other  hand,  become  the  blackest  in  the 
copy,  owing  to  the  rays  passing  freely  through  the 
glass  there,  and  so  producing  the  strongest  effect. 
Accordingly,  I am  obliged  to  have  the  original 

Y 


338 


THE  WONDERS  OF  SCIENCE. 


pictures  painted,  in  the  first  instance,  with  their 
lights  and  shades  reversed,  or  else  I cover  another 
glass  with  a thin  coating  of  isinglass,  and  apply  the 
solution  of  nitrate  of  silver  to  this  ; so  that,  whenj* 
I have  transferred  the  original  picture  by  this  means 
to  a second  plate  of  glass,  in  winch  the  lights  and 
shades  are  the  direct  opposite  to  what  they  are  in 
nature,  I proceed  to  take  a second  copy  of  it — 
but  this  I do  upon  leather,  as  before  explained — 
and  so  obtain  a perfect  reproduction  of  the  origin- 
al, with  all  the  lights  and  shades  in  their  proper 
places. 

“ But  the  same  method  of  copying,”  proceeded 
Mr.  Wedgwood,  “ may  be  applied  to  other  pur- 
poses. It  may  be  rendered  subservient,  for  in- 
stance, for  making  delineations  of  all  such  objects 
as  are  partly  opaque  and  partly  transparent,  such 
as  leaves  and  the  wings  of  insects.  For  this  pur- 
pose it  is  only  necessary  to  put  the  objects  to  be 
copied  between  a plate  of  glass  and  the  prepared 
leather  itself,  when  the  sunlight,  being  more  or  less 
intercepted  by  their  forms,  will  leave  the  figures 
accurately  impressed  upon  the  leather,  so  that  they 
will  appeal'  as  beautiful  white  pictures  upon  a 
black  ground.  There  is,  however,”  added  Mr. 
Thomas  Wedgwood,  “ one  great  defect  connected 
with  the  production  of  sun-pictures  by  the  means  I 
have  described,  and  this  consists  in  the  impossi- 


THE  FIRST  SUN-PICTURES. 


339 


bility  of  fixing  them  so  that  they  shall  be  no  longer 
susceptible  of  being  darkened  when  exposed  to  the 
light.  I have  already  tried  several  methods  of 
obviating  this  difficulty.  I have  covered  the  sun- 
pictures  with  a thin  coating  of  varnish,  but  to  no 
purpose,  for  they  darken  almost  as  rapidly  with 
the  varnish  over  them  as  others  do  without  it. 
Again,  I have  submitted  the  pictures  to  frequent 
washings,  in  the  hopes  of  dissolving  out  of  the 
paper  or  leather  all  the  undec'omposed  nitrate  of 
silver  ; yet,  even  after  this,  a certain  portion  of  the 
active  matter  still  adheres  to  the  white  parts  of  the 
sun-picture,  and  so  causes  them  to  blacken  all  over 
on  being  exposed  to  the  light.  The  consequence 
is,  that  the  pictures  produced  by  the  action  of  the 
sun  must,  in  order  to  be  preserved,  be  examined 
always  in  the  dark,  and  be  kept  continually  in  some 
place  where  no  light  can  penetrate.” 

Humphry  no  sooner  heard  this  than  he  suggested 
a number  of  expedients  by  which  he  fancied  the 
difficulty  might  be  overcome ; and  as  the  lad  ex- 
plained his  reasons  for  the  various  methods  he  pro- 
posed, both  Mr.  Wedgwood  and  his  brother  were 
as  astonished  at  the  extent  of  the  boy’s  knowledge, 
as  they  were  delighted  with  the  acuteness  of  his 
sagacity. 

The  evening  was  passed  in  examining  a portfolio 
of  the  sun-pictures  that  Mr.  Thomas  Wedgwood 
had  brought  wfith  him,  and  Humphry  grew  so 


340 


THE  WONDERS  OF  SCIENCE. 


charmed  with  the  then  entirely  novel  process  of 
“photography that  he  declared  he  would  not  rest, 
until  he  had  investigated  the  matter  himself,  and 
ascertained  experimentally  whether  any  means 
could  be  found  of  rendering  the  pictures  perma- 
nent. 


CHAPTEK  XIV. 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT. 

Our  young  hero  was  still  too  weak  to  leave  the 
house,  for  the  wound  in  his  leg  was  of  so  dan- 
gerous a description  that  Mr.  Borlase  had  strictly 
enjoined  him  to  take  as  little  exercise  as  possible ; 
consequently,  while  Humphry’s  evenings  were  pass- 
ed in  conversation  with  young  Mr.  Watt,  and 
occasionally  the  Wedgwoods,  his  mornings  were 
spent  in  his  chamber  alone,  so  that  he  was  glad  to 
resort  to  study  as  a means  of  enlivening  his  soli- 
tude. 

Still  the  lad  wanted  some  incentive  to  stir  him 
to  enter  upon  a fresh  branch  of  science.  This, 
however,  he  had  now  found  in  the  wonderful  pho- 
tographic impressions  Mr.  Wedgwood  had  shown 
him,  and  he  was  eager  to  make  himself  acquainted 
with  the  laws  of  the  mysterious  principle  by  which 
they  had  been  obtained. 


342 


THE  WONDERS  OF  SCIENCE. 


The  contemplation  of  the  sun-pictures  naturally 
led  Humphry  to  think  of  the  more  transient  pic- 
tures formed  in  the  camera  obscura  by  the  light ; 
and  he  passed  from  the  fixing  of  the  images  to  the 
consideration  of  the  conditions  by  which  the  images 
themselves  are  produced. 

44  How  comes  it,”  he  mentally  inquired,  44  that  a 
piece  of  glass,  merely  because  it  is  rounded  on  one 
or  both  sides,  is  able  to  copy  the  forms  and  colours 
of  external  objects?  And  why  do  several  of  such 
glasses,  in  combination,  bring  the  images  of  even 
the  most  distant  things  so  close  to  us,  that  we  are 
enabled  to  make  out  their  minutest  parts?” 

Humphry  knew  that  the  effect  could  arise  only 
from  some  alteration  in  the  direction  of  the  rays  of 
light  as  they  passed  through  the  glass  itself;  and, 
accordingly,  he  determined  to  set  to  work  and  dis- 
cover the  precise  change  that  a luminous  ray  under- 
goes on  traversing  different  substances. 

In  the  first  place,  however,  it  was  necessary  to 
determine  what  was  the  natural  direction  of  a ray 
of  light  emitted  by  a luminous  body. 

For  this  purpose  Humphry — who  was  still  un- 
able to  undergo  the  exertion  of  arranging  his  own 
experiments — had  to  avail  himself  of  the  assistance 
of  his  sister  Kitty  ; and  so  pleased  was  the  girl  with 
the  office,  that  she  readily  gave  up  to  her  brother 
every  moment  she  could  spare  from  her  household 
duties. 

i 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  343 

Kitty  Davy  was  some  two  years  younger  than 
Humphry  himself,  so  that  they  had  been  infant 
playmates  together,  sharing  the  same  toys  and 
taking  parts  in  the  same  childish  gambols.  It  was 
to  Kitty,  too,  that  the  boy  had  first  recounted  the 
fairy  stories  he  loved  to  invent;  and  when,  in  his 
after-youth,  Humphry  compounded  his  celebrated 
“thunder-powder,”  Kitty  invariably  aided  him  in 
the  manufacture  of  the  composition:  so  that  each 
year  had  served  to  increase  the  love  which,  from 
the  remembrance  of  the  pleasures  they  had  enjoyed 
together,  had  been  begotten  almost  with  the  dawn 
of  memory  itself. 

Kitty  was  now  budding  into  womanhood.  She 
had  grown  so  tall  within  the  last  year,  that  her  fig- 
ure was  spare,  and  not  particularly  comely ; while 
the  curls,  which  once  fell,  with  childish  beauty, 
in  tortuous  profusion  about  her  neck,  had  now  been 
displaced,  and  her  hair  twisted  into  the  more  wo- 
manly, but  less  gainly,  protuberance  at  the  back. 
This  style  of  head-dress  had  long  been  a point  of 
ambition  with  the  young  lady,  and  now  that  she 
had  risen  to  the  dignity  of  wearing  her  hair  like 
her  mother,  Miss  Kitty  had  grown  to  fancy  that 
she  was  no  longer  a child. 

Nor  was  she.  The  increasing  strength  of  her 
affection  for  her  brother  showed  that  her  woman’s 
nature  was  developing,  and  she  seemed  to  cling  to 
Humphry  and  her  mother  with  a new  tenderness, 


344 


THE  WONDEES  OF  SCIENCE. 


as  if  she  needed  some  one  to  heap  her  strengthened 
love  upon.  The  doll  upon  which  she  had,  until 
the  last  year  or  so,  bestowed  her  caresses,  had  been 
given  to  one  of  her  younger  sisters ; and  now  she 
appeared  to  take  almost  a mother’s  pride  in  tending 
little  Johnny,  her  brother,  instead. 

Humphry  during  his  illness  had  been  constantly 
“ nursed”  by  her,  and  now  that  she  was  allowed  to 
officiate  in  the  kitchen,  the  girl  loved  to  surprise 
him  each  day  with  some  new  posset  or  jelly  which 
she  had  prepared  for  his  gratification.  She  had  read, 
to  him,  too,  so  long  by  liis  bedside  from  the  scientific 
books  which  her  brother  loved  to  listen  to,  that? 
aided  by  his  explanations  of  the  more  difficult  parts 
of  the  subject,  she  herself  had  acquired  a slight 
knowledge  of  the  phenomena  of  the  universe : so 

that,  while  assisting  him  in  his  experiments,  she  felt 

* 

almost  the  same  taste  for  the  work  as  Humphry 
did,  and  was  not  a little  delighted  when  the  hour 
came  for  her  to  take  her  accustomed  post  in  her 
brother’s  sick  chamber. 

Humphry,  as  we  said,  was  intent  upon  discov- 
ering the  natural  direction  of  a ray  of  light  pro- 
ceeding from  a luminous  body.  With  this  view 
he  got  Kitty  to  close  the  shutters  so  as  to  com- 
pletely darken  the  room,  and  then  to  pierce  a fine 
hole  through  them.  This  being  done,  Humphry 
pointed  out  to  the  girl  that  the  beam  was  in  a 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  845 

perfectly  straight  line — for  the  course  of  it  was 
rendered  plain  by  the  little  particles  of  dust  that 
floated  in  the  atmosphere,  flashing,  as  they  danced 
in  the  ray,  like  so  many  tiny  fire-flies.  Then  as 
Kitty  wheeled  her  brother’s  chair  so  that  the  light 
fell  directly  upon  his  eye,  the  boy  could  see  the  sun 
itself  shining  through  the  hole;  thus  proving  that 
the  beam  proceeded  in  a direct  straight  line  from 
the  orb  of  light  to  him. 

The  next  step  was  to  procure  a flexible  tube,  and 
with  this  held  straight  before  the  eye,  Humphry 
could  still  distinguish  the  sun  through  the  hole  in 
the  shutter,  though  when  the  tube  was  curved  the 
effect  was  totally  different,  for  then  no  light  at  all 
could  be  perceived. 

Kitty  was  not  a little  delighted  with  the  demon- 
stration that  a ray  of  light  proceeds  in  a straight 
line;  and  Humphry,  to  make  her  understand,  as 
well  as  to  prove  to  himself  experimentally,  that 
all  luminous  bodies  projected  an  infinity  of  such 
straight  rays  in  every  possible  direction , bade  the  will- 
ing girl  Ltch  him  the  rushlight  and  shade  from  be- 
low. 

While  the  shutters  were  still  closed  the  candle 
was  lighted,  and  then  Humphry  pointed  out  to  his 
sister  how  the  little  luminous  circles  that  were 
spattered  over  the  wall  all  round  the  room,  as  the 
light  passed  through  the  holes  in  the  shade,  showed 
that  the  rays  proceeded  from  it  in  every  direc- 


346  THE  WONDERS  OF  SCIENCE. 

tion ; and  that  they  travelled  in  a straight  course 
was  easily  proved,  by  covering  with  the  finger  any 
one  of  the  holes  in  the  shade,  when  the  lumin- 
ous circle  on  the  wall,  which  was  in  a direct  line 
with  the  hole,  and  the  flame  became  immediately 
obscured. 

It  was  plain,  then,  that  a ray  of  light  travelled 
naturally  in  a straight  line.  Still,  as  a further 
proof  of  this  phenomenon,  Humphry  threw  the  shad- 
ow of  an  opaque  body,  of  a certain  size,  upon  a 
white  screen,  and  there  measured  its  dimensions. 
Having  cut  a piece  of  millboard,  exactly  a foot 
square,  he  placed  it  1 foot  distant  from  the  flame 
of  a candle,  and  then  arranging  the  screen  at 
double  the  distance,  or  two  feet  from  the  light,  he 
found  upon  measuring  the  shadow  of  the  mill- 
board that  it  was 'exactly  (2x2)  4 times  larger 


than  the  millboard.  When  the  screen  was  three 
feet  distant  from  the  candle,  or  3 times  as  far 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  347 

from  the  light  as  the  millboard,  the  shadow  was 
ascertained  to  be  (3x3)  9 times  larger  than  the 
surface  from  which  it  was  projected ; while  at  the 


distance  of  4 feet,  the  dark  space  upon  the  screen 
was  discovered  to  be  (4x4)  1G  times  greater  than 
the  millboard  itself. 


This  effect  could  arise  solely  from  the  rays  of  the 
candle  proceeding  in  a straight  direction,  as  will  be 
rendered  evident  by  the  preceding  diagrams  ; where 
it  will  be  seen  that  the  opaque  body,  interposed  be- 
tween the  light  and  the  screen,  prevents  the  rays 


348 


THE  WONDERS  OF  SCIENCE. 


which  fall  upon  it  reaching  the  screen  itself,  so  that 
a dark  space  appears  upon  the  latter,  as  many  times 
larger  than  the  opaque  body,  as  the  distance  of  the 
screen  from  the  candle  is  greater  than  the  body 
projecting  the  shadow ; for  it  is  manifest,  that  if  a 
series  of  right  lines  be  drawn  from  the  luminous 
point  to  the  edges  of  the  opaque  body,  and  thence 
to  the  screen  itself,  they  will  exactly  circumscribe  a 
space  whose  dimensions  will  be  proportional  to  the 
distance  of  the  one  to  the  other. 

“Well,”  said  Humphry  to  his  sister,  “we  now 
see  that  luminous  bodies  emit  rays  of  light  in  all 
directions , and  that  each  ray  from  them  proceeds 
in  a straight  line,  while  those  substances  which 
are  called  opaque  prevent,  when  placed  before  the 
light,  the  rays  from  reaching  other  substances  be- 
hind them — the  rays,  in  such  cases,  being  stopped 
or  intercepted.  Some  bodies,  however,”  added 
the  boy,  “ are  capable  of  transmitting  the  rays  of 
light:  that  is  to  say,  they  allow  the  beams  to  pass 
through  them,  and  these  are,  therefore,  termed 
transparent ; since,  unlike  opaque  bodies,  they  pro- 
ject no  shadows  when  placed  between  the  light 
and  other  bodies.  Let  us  now  see  what  occurs 
when  a ray  of  light  passes  through  a transparent 
body.” 

Accordingly,  Humphry  procured  a small  open 
vessel,  in  one  of  the  sides  of  which  there  was  a hole 
near  the  top,  large  enough  to  admit  the  light  from 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  349 

a candle.  The  lad  then  proceeded  to  ascertain  the 
exact  place  where  the  ray  of  light  from  the  flame 
fell  at  the  bottom  of  the  vessel;  and  found  that, 
when  the  vessel  was  empty  and  the  candle  placed 
at  a short  distance  from 
the  hole,  there  was  a 
small  circle  of  light 
formed  at  the  bottom, 
which  was,  of  course,  a-' 
in  a direct  line  with  the  hole  and  the  flame,  as  here 
shown. 

Having  then  set  a mark  at  A,  where  the  circle 
of  light  appeared,  he  directed  Kitty  to  pour  water 
into  the  vessel  until  it  was  half  full ; and  when  she 
had  done  so,  he  noticed  that  the  ray  of  light  from 
the  candle  no  longer  fell  upon  the  same  spot  as  it 
did  when  the  vessel  was  empty,  but  at  a little  dis- 
tance nearer  the  candle,  so  that  it  was  plain  that 

the  ray,  instead  of  pro- 
ceeding in  a straight 
x line  as  before,  had,  in 
passing  through  the 
water,  been  bent  down 
out  of  its  usual  course , 
in  the  manner  indicated  at  B. 

“You  see,  then,”  remarked  Humphry,  “that  a 
ray  of  light,  when  it  falls  in  a slanting  direction 
upon  a transparent  body,  no  longer  travels  on  in  a 
straight  line , but  is  re  fracted,”  as  it  is  called,  “ or  bent 


350 


THE  WONDEKS  OF  SCIENCE. 


out  of  its  previous  course , at  a certain  angle.  Conse- 
quently, if  the  spot  B was  a fish  lying  at  the  bot- 
tom of  a river,  it  would  be  seen  by  a person  on  the 
shore  in  the  direction  of  the  point  A;  and  thus  it 
would  appear  out  of  its  true  place,  and,  in  order  to 
strike  it  with  a spear,  we  should  have  to  direct  the 
weapon  at  a spot  nearer  to  us  than  where  the  fish 
seemed  to  be  lying.” 

Then  her  brother  told  her  that  it  was  for  the 
same  reason  that  a straight  stick  appeared  to  be 
crooked  when  half  immersed  in  a pool  of  water, 
and  a crooked  stick  a straight  one  under  the  same 
circumstances ; “ for,”  said  he,  “ if  instead  of  the 
straight  ray  of  light  we  imagine  a straight  stick  to 
be  passed  through  the  hole,  so  that  the  point  of  it 
may  be  at  the  spot  A,  it  is  plain  that  in  the  water 
the  end  of  the  stick  will  appear  at  B,  since  the  part 
of  it  which  is  immersed  will  seem  to  be  bent  in  that 
direction  ; whereas  if  the  stick  itself  be  bent,  so  that 
the  end  of  it  is  at  B,  it  will,  for  the  same  reason, 
appear  when  in  the  water  at  A,  and,  consequently, 
seem  to  be  perfectly  straight. 

The  next  step  was  to  try  and  measure  the  degree 
of  refraction,  or,  in  other  words,  to  find  out  how 
much  a ray  of  light  was  bent  out  of  its  usual 
course  on  passing  through  different  transparent  sub- 
stances. 

Accordingly,  Humphry  procured  his  old  school- 
slate,  and  having  managed,  with  Kitty’s  assistance, 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  351 


to  mount  this  on  a heavy  pedestal,  he  described 
upon  the  slate  a circle  with  two  diameters,  each 
perpendicular  to  the  other;  then  having  bored  a 
hole  in  the  centre,  he  fitted  into  it  a large  cork; 
this  had  a straight  tube  afterwards  let  into  it,  so 
that  the  tube,  by  means  of  the  cork  in  the  middle, 
could  be  moved  freely  round  » 


the  circle,  turning,  as  it  did, 
upon  the  centre  of  it.  The 
whole  apparatus  was  then  in- 
serted in  a vessel  of  water,  so 


that  the  fluid  reached  exactly  ^ 
to  the  level  of  the  horizontal 


diameter — thus,  without  touching  the  end  of  the 
tube. 

The  youth  then  found,  that  when  the  tube  A 
was  directly  perpendicular  to  the  surface  of  the 
water,  a ray  of  light,  on  passing  down  it,  suffered 
no  change  at  all  in  its  direction ; and  that  on  plac- 
ing a sixpence  in  the  water,  exactly  in  a line  with 
the  perpendicular  diameter,  B,  it  could  be  seen  dis- 
tinctly through  the  tube,  so  that  the  rays  from  the 
coin,  on  quitting  the  water,  proceeded  in  the  same 
straight  course  as  they  had  pursued  while  passing 
through  the  fluid. 

Hence  it  was  evident  that  a ray  of  light,  on 

entering  or  quitting  a refracting  surface  in  a per- 
pendicular line,  is  not  refracted  or  bent  out  of  its 


course. 


352  THE  WONDERS  OF  SCIENCE. 

It  was  different,  however,  when  the  tube  was 

slanted , instead  of  being  placed 
straight  above  the  surface  of 
the  water,  for  when  a ray  of 
light  passed  down  it  in  that 
direction,  the  ray  was  found 
to  be  refracted,  or  bent  out  of 
a straight  course,  as  shown 
in  the  above  diagram. 

Now  the  precise  direction  of  the  refracted  ray 
having  been  marked  upon  the  slate,  the  apparatus 
was  removed  from  the  water,  and  the  distance  of 
the  tube  A from  B,  the  vertical  diameter,  meas- 
ured, as  well  as  the  distance  of  the  refracted  ray, 

a , from  the  same  perpendicular  line,  b,  and  it 
was  then  found  that  the  refracted  ray,  a , was 
as  near  as  possible  3 inches  from  the  diameter, 

b,  while  the  ray  A,  which  passed  down  the  tube, 
was  as  much  as  4 inches  distant  from  B,  the  same 
line. 

The  tube  A was  then  set  at  about  1 J inches  from 
the  diameter  B,  and  the  apparatus  replaced  in  the 
water,  when  it  was  discovered  that  a ray  of  light,  a , 
on  passing  down  it,  fell  exactly  at  1 inch  from  b , the 
perpendicular  line. 

Several  other  positions  of  the  tube  were  afterwards 
tried,  and  invariably  with  the  same  result : let  the 
tube  be  slanted  as  it  might,  the  distance  A . . . B 
of  the  ray  which  passed  down  it,  when  compared 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  353 

with  the  distance  a ...  b of  the  refracted  ray  from 
the  perpendicular  line,  was  always  ascertained  to  be  in 
the  same  proportion — viz.  very  nearly  as  1^  to  1 ; or, 
more  correctly  speaking,  when  A . . . B,  the  sine  of 
the  angle  at  which  the  ray  entered  the  water,  was 
1^,  then  «...  5,  the  sine  of  the  angle  formed  by  the 
refracted  ray,  was  exactly  1. 

On  referring  to  his  books,  Humphry  found  that 
the  number  1 13030fi0-  constituted  what  was  termed  the 
index  of  refraction  for  water. 

On  performing  the  same  experiment  with  oil  of 
turpentine  the  lad  discovered,  that  when  the  ray 
which  passed  down  the  tube  was  almost  as  much 
as  1-|-  inch  distant  from  the  perpendicular,  the  re- 
fracted ray  was  1 inch  distant  from  the  same  line ; 
whereas  with  sulphuret  of  carbon  (though  with 
this  the  experiment  was  performed  on  a smaller 
scale),  when  the  ray  passing  down  the  tube  was 
l-§  inch  removed  from  the  perpendicular — the  re- 
fracted ray  was  still  only  1 inch  away  from  the 
same  line. 

Humphry  then  consulted  a table  of  the  refractive 
power  of  different  bodies,  and  learned  that  hydrogen 
gas  is  the  least  refractive  of  all  known  substances 
(that  is  to  say,  a ray  of  light  passing  through  this 
gas  is  bent  down  by  it  out  of  its  previous  course, 
less  than  by  any  other  known  body),  and  that  the 
diamond  has  very  nearly  the  greatest  refractive  pow- 
er of  all,  while  the  refraction  of  the  air  in  its  ordi- 

Z 


354 


THE  WONDERS  OF  SCIENCE. 


nary  state  is  only  294  millionths  greater  than  that 

of  a vacuum. 

This,  however,  is  the  refractive  power  of  the  at- 
mosphere at  its  average  density  near  the  earth’s  sur- 
face. But  we  learn  from  the  barometer  that  the 
density  of  the  air  diminishes  as  we  mount  above  the 
earth,  and  it  has  been  found  by  experiment  that  the 
refractive  power  of  the  atmosphere  decreases  in 
proportion  as  it  becomes  more  and  more  rarified; 
so  that  the  atmospheric  refraction  is  greatest  at 
the  earth’s  surface,  and  gradually  diminishes  up- 
wards, till  the  air  becomes  so  rare  as  to  be  able  to 
produce  scarcely  any  effect  at  all  upon  the  rays  of 
light. 

“ In  order  to  understand 
this,”  said  Humphry  to  his 
sister,  “ we  must  consider  the 
earth  to  be  encased  in  a series 
of  shells,  as  it  were,  of  atmos- 
phere, each  of  a less  density 
than  the  one  below  it,  and, 
consequently,  of  a less  refractive  power — thus. 

“ Let  us  suppose,”  the  lad  continued,  “ the  round 
ball  in  the  centre  here  to  represent  the  earth,  and 
the  ring  of  atmosphere  immediately  next  to  it  to 
have  a refractive  power  nearly  300  millionths  great- 
er than  a vacuum ; and  the  refractive  power  of  the 
ring,  or  shell  of  atmosphere  immediately  above  this, 
to  be  equal  to  only  200  millionths  compared  with 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  355 

the  same  standard,  while  the  power  of  the  third 
ring  decreases  to  100  millionths,  and  that  of  the 
outer  one  to  50  millionths,  whereas  beyond  this  no 
refraction  whatever  exists,  so  that  the  rays  moving 
through  free  space  will  continue  in  the  same  line 
as  that  in  which  they  are  emitted  from  the  sun. 
What,  then,  will  be  the  effect  of  such  a series  of  at- 
mospheric shells  upon  a ray  of  light  passing  through 
them?” 

To  illustrate  this  Humphry  drew  the  lines  here 
shown  through  the  following  diagram. 

“The  orb  S,  outside  the  earth,”  continued  Hum- 
phry, “ represents  a 

the  sun  below  the 
horizon,  emitting, 
let  us  suppose,  his 
rays  in  all  direc- 
tions. These,  pass- 
ing through  free 
space,  proceed  on- 
wards in  a perfectly  straight  line ; and  one  of  them 
is  here  made  to  fall  upon  the  outer  ring  of  the 
earth’s  atmosphere,  where  it  is  slightly  refracted,  or 
bent  down  out  of  its  former  course,  so  that,  instead 
of  continuing  in  the  direction  of  the  dotted  line  a,  it 
proceeds  through  the  upper  portion  of  our  atmos- 
phere in  the  direction  of  the  unbroken  line,  until  it 
reaches  a part  of  the  atmosphere  of  greater  density 
— as  in  the  second  ring ; when,  instead  of  going  on 


356 


THE  WONDERS  OF  SCIENCE. 


in  the  direction  of  the  second  dotted  line  b,  it  is  again 
refracted,  or  bent  down,  in  a greater  degree  than  be- 
fore. Then  travelling  onwards,  it  reaches  the  third 
ring,  where  the  atmosphere,  being  of  a still  greater 
density,  and,  consequently,  having  a greater  refract- 
ive power,  it  is  once  more  bent  out  of  its  course  c, 
and  that  to  a still  greater  extent  than  before.  In 
this  manner  it  ultimately  arrives  at  a stratum  of  at- 
mosphere which  immediately  envelopes  the  surface 
of  the  earth,  and  which,  having  the  greatest  density 
of  all,  has  the  greatest  refractive  power ; so  that  the 
ray,  instead  of  continuing  in  the  direction  d,  is  here 
bent  down  more  than  ever,  and  finally  reaches  the 
eye  in  the  direction  e,  which  is  in  a direct  line  with 
the  orb  s.  The  consequence  is,  that  as  every  object 
is  seen  in  the  direction  that  the  ray  has  at  the  instant 
of  arriving  at  the  eye , the  sun  itself  appears  to  be 
above  the  horizon  when  it  is  positively  below  it, 
as  at  S ; so  that,  by  the  refraction  of  the  atmos- 
phere, the  sun  is  seen  by  us  before  he  rises  in  the 
morning,  and  for  a short  time  after  he  sets  in  the 
evening.” 

Kitty  was  so  astonished  at  the  above  conclusion, 
that,  though  she  understood  the  explanation,  she 
told  her  brother  that  she  could  hardly  help  doubt- 
ing the  fact ; saying,  “ it  was  almost  the  same  as 
asserting  that  we  could  see  a thing  that  was  out  of 
sight.” 

Humphry  undertook  to  prove  to  his  sister,  by 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  357 


experiment,  that  such  a result  was  quite  possible  by 
refraction. 

Accordingly,  he  bade  Kitty  place  the  wash-hand 
basin  upon  the  table,  and  then  having  deposited  a 
shilling  at  the  bottom  of  it,  he  told  the  girl  herself 
to  recede  from  the  table  until  the  edge  of  the  basin 
obscured  the  shilling  from  her  sight ; and  when 
Kitty  assured  him  that  she  could  no  longer  see  the 
coin,  he  poured  some  water  into  the  vessel,  and 
immediately  the  girl  exclaimed — “Dear,  dear, 
how  odd ! I can  see  the  shilling  quite  plainly 
now.” 

“You  perceive,  then,  Miss  Kitty,”  cried  the  boy, 
triumphantly,  “ it  is  quite  possible  by  refraction  to 
see  things  that  are  out  of  sight,  for  the  ray  from 
the  shilling,  A,  on  passing  out  of  the  water  into 
the  air,  is  bent  out  of  its 

course,  and  you  behold  it  in  ^ 

the  direction  of  the  line  in 
which  it  enters  your  eye — 
thus,  at  a. 

“But  far  more  wonderful  things  than  this  have 
been  brought  to  pass  by  the  same  means,  Kitty,” 
said  her  brother,  delighted  to  impart  the  knowl- 
edge he  had  obtained  from  his  books  on  this 
subject,  “and  these  are  what  are  called  mirages , 
or  optical  illusions,  produced  by  extraordinary  re- 
fractions in  the  atmosphere.  For  instance,  the 
cliffs  on  the  French  coast  are  50  miles  distant 


a A 


358 


THE  WONDERS  OF  SCIENCE, 


from  Hastings,  on  the  coast  of  Sussex,  and  they  are 
actually  hidden  from  the  eye  by  the  convexity  of 
the  earth ; that  is  to  say,  a straight  line  drawn 
from  Hastings  to  Calais  or  Boulogne  would  pass 
through  the  sea.  A year  or  two  ago,  however, 
Mr.  Latham,  a Fellow  of  the  Tioyal  Society,  who 
was  residing  at  Hastings,  was  surprised  to  see  a 
crowd  of  people  running  to  the  sea-side.  Upon  in- 
quiry into  the  cause  of  this,  he  was  informed  that 
the  coast  of  France  could  be  seen  by  the  naked 
eye.  He  immediately  went  down  to  the  shore  to 
witness  so  singular  a sight,  and  there  discovered 
distinctly  the  French  cliffs  extending  for  some 
leagues  along  the  horizon,  and  so  vividly  that  they 
appeared  to  be  only  a few  miles  off.  The  sailors 
and  fishermen,  with  whom  Mr.  Latham  walked 
along  the  water’s  edge,  could  hardly,  at  first,  be  per- 
suaded of  the  reality  of  the  appearance  ; but  as  the 
cliffs  gradually  became  more  elevated,  they  were  so 
convinced  that  they  pointed  out  to  Mr.  Latham  the 
different  places  they  had  been  accustomed  to  visit: 
such  as  the  bay  and  the  windmill  at  Boulogne,  St. 
Vallery,  and  other  places  on  the  coast  of  Picardy, 
even  as  far  as  Dieppe,  all  the  French  shores  ap- 
pearing to  the  English  sailors  as  if  they  were  sailing 
at  a short  distance  from  them  towards  the  harbours. 
With  the  aid  of  a telescope  the  French  fishing-boats 
were  plainly  seen  at  anchor,  and  the  different  colours 
of  the  land  upon  the  heights,  together  with  the  build- 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  359 

ings,  were  perfectly  discernible.  The  day  when  this 
occurred  is  said  to  have  been  extremely  hot,  without 
a breath  of  wind  stirring,  and  the  phenomenon  con- 
tinued visible  in  the  highest  splendour  until  past  8 
o’clock  in  the  evening,  having  been  seen  for  three 
hours  continuously.” 

Some  few  years  after  the  date  of  the  above,  a no- 
less-marvellous  optical  illusion  was  seen  by  Profess- 
or Yince  of  Cambridge,  in  company  with  another 
gentleman,  at  Ramsgate.  Between  this  town  and 
Dover  there  is  a hill,  on  the  farther  side  of  which 
stands  Dover  Castle,  the  summits  of  whose  four  tur- 
rets can,  in  ordinary  states  of  the  atmosphere,  be 
just  seen  projecting  above  the  brow,  while  the  body 
of  the  castle  itself  is  usually  hidden  from  view  by 
the  rising  earth  between  it  and  Ramsgate.  On  the 
evening  of  the  6th  of  August,  1806,  however,  when 
the  air  was  very  still,  and  a little  hazy,  not  only 
were  the  tops  of  the  four  towers  of  the  castle 
visible  above  the  brow  of  the  hill  in  the  distance, 
but  the  whole  of  the  castle  itself  appeared  trans- 
ferred to  the  side  of  the  hill  next  Ramsgate,  as  if 
it  had  been  really  built  there,  instead  of  on  the 
other  side  of  the  eminence.  This  phenomenon  was 
so  singular  and  unexpected  that  Dr.  Yince,  at 
first  sight,  thought  it  an  illusion.  On  continuing 
his  observations,  however,  he  became  satisfied  that 
what  he  saw  was  a real  image  of  the  castle.  To 
assure  himself  that  it  was  no  deception,  he  gave  the 


360 


THE  WONDERS  OF  SCIENCE. 


telescope  to  a gentleman  who  was  with  him  at  the 
time,  and  who  also  saw  the  same  clear  image  of  the 
entire  castle,  situate  on  the  near  side  of  the  hill,  as 
the  Doctor  himself  had  witnessed.  The  view  of 
the  castle  was  very  strong,  and  well  defined ; and 
though  the  rays  from  the  farther  side  of  the  hill 
must,  undoubtedly,  have  reached  the  eye  at  the 
same  time,  still  the  strength  of  the  image  of  the 
castle  itself  so  far  obscured  the  background  that  it 
made  no  sensible  impression  on  the  spectators.  Dr. 
Vince  continued  to  observe  the  image  for  about 
20  minutes,  during  which  time  the  appearance  re- 
mained precisely  the  same,  but  rain  then  came  on, 
and  he  was  prevented  making  any  further  observa- 
tions. 

Humphry  now  began  to  study  how,  by  means  of 
extraordinary  refraction,  inverted  images  of  objects 
might  be  seen  in  the  atmosphere. 

With  this  view  he  drew  the  subjoined  diagram, 


u There,  Kitty,”  said  the  lad,  as  he  laid  down 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  3 tjl 


his  pencil  and  compasses,  “the  drawing  represents 
a ship  below  the  horizon,  and  concealed  from 
the  eye  of  an  observer  by  the  convexity  of  the 
earth.  Well,  if  we  suppose  the  refractive  power 
of  the  air  at  a little  above  the  earth’s  surface  to  be 
less  than  it  is  at  the  surface  itself,  then  the  rays 
which  proceed  upward  from  the  ship,  and  which 
never  could,  in  the  ordinary  state  of  the  atmosphere, 
reach  the  eye  in  the  position  here  shown,  will  be 
refracted  into  curved  lines,  so  that  they  will  cross 
one  another ; while  the  ray  which  came  from  the 
masthead,  instead  of  being  uppermost,  will  change 
places  with  that  coming  from  the  hull,  and  becom- 
ing the  undermost  of  the  two,  will  enter  the  eye  in 
that  position : consequently,  as  every  object  is  seen, 
as  I said  before,  in  the  direction  of  the  rays  at  the 
moment  of  their  arriving  at  the  eye , without  reference 
to  their  previous  course , an  inverted  image  of  the 
ship  will  be  perceived  in  the  air,  in  the  direction  of 
the  dotted  lines,  and  thus  appear  elevated  above  the 
horizon.” 

Kittv  said  she  could  hardly  follow  the  explana- 
tion, and  wished  to  know  whether  her  brother  could 
not  devise  some  experiment  in  proof  of  it. 

After  a few  moments’  consideration,  Humphry 
requested  his  sister  to  fetch  him  a square  phial, 
and  to  make  him  a little  clear  syrup  with  some 
lump-sugar  and  water.  When  this  was  prepared, 
the  boy  poured  a small  quantity  of  the  syrup  into 


3b2 


THE  WONDERS  OF  SCIENCE. 


the  phial,  and  upon  this  again  he  poured  very  care- 
fully an  equal  quantity  of  pure  water,  so  that  it 
might  float  upon  the  syrup.  Now  the  syrup,  being 
a fluid  of  greater  density  than  the  water,  had  a pro- 
portionately greater  refractive  power,  and  as  the 
two  combined  with  each  other  they  formed  strata, 
having  different  refractive  powers,  the  same  as  those 
which  had  been  supposed  to  exist  in  the  atmosphere 
at  certain  times,  at  a little  distance  above  the  sur- 
face of  the  earth.  Then  having  printed  the  word 
Syrup  upon  a card,  Humphry  held  this  behind  the 
bottle,  and  the  letters  were  seen  erect  through  the 
stratum  of  syrup  at  the  bottom,  but  upside  down  at 
the  part  where  the  syrup  was  mixing  with  the  wa- 
ter, and  erect  again  through  the  layer  of  water  itself 
at  the  top. 

After  this  the  lad  poured  the  same  quantity  of 
spirits  of  wine  carefully  over  the  water  itself,  so  that 
the  spirit  being  lighter  than  this  might  float  above 
this  again ; and  then  having  printed  the  word  Spirit 
on  the  upper  part  of  the  same  card,  the  letters  of 
this  were  seen  erect  through  the  layer  of  water,  but 
topsy-turvy  at  the  part  where  the  spirit  and  water 
were  mingling,  and  in  their  proper  form  through  the 
uppermost  stratum  of  spirit  itself. 

Humphry  afterwards  produced  the  same  effect  by 
holding  a heated  iron  above  a tumbler  of  water,  so 
that  the  upper  surface  of  it  became  warmed  while 
the  lower  remained  cold,  and  the  portion  in  the  mid- 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT. 

die  became  tepid.  The  lieat,  therefore,  expanded, 
and  so  rendered  rarer  the  upper  portions  of  the 
liquid ; and  as  it  forced  its  way  downwards,  pro- 
duced strata  of  different  densities,  and,  consequent- 
ly, of  different  refractive  powers.  The  result  was, 
that  on  looking  through  the  glass  vessel  three  im- 
ages were  seen  as  before ; the  upper  and  the  lower 
ones — which  arose  from  the  rays  passing  through 
the  colder  and  the  warmer  strata — being  erect, 
and  the  middle  one,  or  that  which  proceeded  from 
the  rays  passing  through  the  portion  in  the  mid- 
dle, being  inverted — as  previously  observed.  The 
same  effect  may  be  produced  by  looking  along  the 
side  of  a red-hot  poker,  at  an  object  10  or  12  feet 
off,  when  an  inverted  image  will  be  seen  at  the 
distance  of  about  -§ tlis  of  an  inch  from  the  line  of 
the  poker,  and  an  erect  image  within  and  without 
this. 

The  youth,  having  now  demonstrated  to  his  sis- 
ter how  it  was  possible  to  produce  three  distinct 
images,  and  one  of  these  inverted,  from  the  same 
object,  when  seen  through  strata  of  different  dens- 
ities, proceeded  to  recount  to  Kitty  stories  of  sim- 
ilar phenomena  observed  at  sea.  He  told  her  how 
Dr.  Vince  had  seen  at  Kamsgate  a ship  wdiose  top- 
masts only  were  visible  above  the  horizon,  while 
over  this,  in  the  air,  two  images  of  the  complete 
ship  were  observed,  the  uppermost  being  erect , and 
the  under  one  inverted , with  the  pennant  from  the 


364 


THE  WONDERS  OF  SCIENCE, 


masthead  of  the  inverted  image  nearly  touching  that 
from  the  real  ship,  seen  peeping  above  the  horizon. 
This  was  distinctly  visible  through  the  telescope ; 
the  sea  appearing  between  the  two  ships  in  the  air, 
as  here  represented : 


“As  the  ship  rose  to  the  horizon,”  said  Hum- 
phry, “the  upper  image  gradually  disappeared,  and 
while  this  was  going  on  the  lower  and  inverted 
image  as  gradually  descended ; but  the  mastheads 
of  the  real  and  the  spectral  inverted  ship  never 
exactly  touched.  On  the  real  ship  becoming  en- 
tirely visible,  the  aerial  images  were  found  to  have 
been  perfect  representations  of  it,  even  though  the 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  365 

whole  of  the  vessel  at  the  time  must  have  been  con- 
cealed below  the  horizon.” 

There  is,  however,  it  may  here  be  added,  a still 
more  marvellous  story  in  connexion  with  this  part 
of  the  subject,  though  it  occurred  at  a more  recent 
date  than  that  recounted  by  Humphry.  During  a 
voyage  to  the  coast  of  Greenland  in  the  year  1822, 
Captain  Scoresby,  having  seen  an  image  of  an  in- 
verted ship  in  the  air,  directed  his  telescope  to  it, 
and  was  able  to  discover  that  it  was  his  father’s 
vessel , which  was  at  the  time  below  the  horizon , and 
cruising  in  a neighbouring  inlet.  “ The  image,” 
says  the  captain,  “ was  so  well  defined  that  I could 
distinguish  by  a telescope  every  sail,  the  general 
‘rig  of  the  ship,’  and  its  particular  character,  in- 
somuch that  I confidently  pronounced  it  to  be 
my  father’s  ship  the  6 Fame,’  which  it  afterwards 
proved  to  be;  though,  on  comparing  notes  with 
my  father,  I found  that  our  relative  position  at  the 
time  gave  our  distance  from  one  another  30  miles, 
which  is  about  17  miles  beyond  the  horizon,  and 
some  leagues  beyond  the  limit  of  direct  vision.  I 
was  so  much  struck  by  the  peculiarity  of  the  cir- 
cumstance,” adds  the  captain,  “ that  I mentioned  it 
to  the  officer  of  the  watch,  stating  my  full  convic- 
tion that  the  ‘ Fame’  was  then  cruising  in  the  neigh- 
bouring inlet.” 

The  same  officer,  while  navigating  the  Green- 
land sea  in  1820,  saw  the  images  of  several  ships 


366 


THE  WONDERS  OF  SCIENCE. 


in  the  air.  Some  of  these  were  double,  and  in- 
verted, while  along  with  them  there  appeared  aerial 
images  of  the  ice,  in  two  strata;  the  highest  of 
which  had  an  altitude  of  a quarter  of  a degree. 

The  representation  of  ships  in  the  air  by  un- 
equal refraction  has,  no  doubt,  given  rise  in  early 
time  to  the  superstitions  of  phantom-ships,  which 
are  always  said  to  sail  in  the  eye  of  the  wind,  and 
to  plough  their  way  through  the  sea  when  there  is 
not  a breath  of  wind  to  ruffle  its  surface.  The 
story  of  the  “Flying  Dutchman”  had,  probably,  a 
similar  origin ; and  the  legend  of  the  wizard  beacon- 
keeper  of  the  Isle  of  France,  who  saw  in  the  air  the 
vessels  bound  to  the  island  long  before  they  were 
visible  in  the  horizon,  doubtlessly  arose  from  the 
man’s  observation  of  some  such  phenomena. 


CHAPTER  XV. 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT 

(i continued ). 

Young  Humphry  now  sought  to  discover  the 
circumstances  upon  which  the  formation  of  images, 
or  pictorial  representations  of  objects,  depends. 

“In  the  first  place,”  said  he  to  his  sister,  “you 
must  bear  in  mind  that  all  objects  throw  off  from 
them,  in  all  directions,  rays  of  light,  which  are  of 
the  same  colour  as  the  objects  themselves.  The  sol- 
dier’s coat  appears  red  to  us,  because  it  sends  red 
rays  to  the  eye;  the  fields  are  green,  because  they 
emit  rays  of  green  light ; and  the  summer  clouds  are 
white,  because  the  light  they  reflect  to  us  is  of 
that  colour.  Indeed  every  flower,  whatever  may  be 
its  tint,  is  seen  by  us  coloured  as  it  is  merely  be- 
cause the  rays  of  light  proceeding  from  it  are  of 
the  same  hue  as  the  flower  itself  appears  in  our 
eyes 


368 


THE  WONDERS  OF  SCIENCE. 


Kitty  told  Humphry  that  she  could  hardly  com- 
prehend this ; saying,  “ that  the  pattern  of  the 
paper  on  the  wall  was  green  and  yellow,  and  yet, 
let  her  look  at  it  in  whatever  way  she  might, 
she  could  seen  no  green  and  yellow  rays  coming 
from  it.” 

Her  brother,  however,  assured  her  that,  if  no 
rays  from  the  paper  entered  her  pupil,  she  would 
not  be  able  to  see  it  at  all ; that  is  to  say,  the  wall 
would  appear  absolutely  black  in  her  eyes ; whereas, 
if  the  rays  it  reflected  were  colourless , it  would  seem 
perfectly  white  to  her. 

“ In  ancient  times,”  continued  Humphry,  “ it 
was  believed  that  the  eye  itself  had  some  peculiar 
power  of  emitting  light,  and  thus  of  distinguishing 
objects  by  its  own  agency ; but  now  we  know  that 
no  such  power  resides  in  the  organ  of  sight,  the 
eye  being  almost  passive  during  vision,  and  see- 
ing only  those  objects  which  emit  or  reflect  rays 
of  light  to  it : for  it  is  merely  by  such  rays  of  light 
entering  the  pupil,  and  forming  a ^picture  of  the 
object  at  the  back  of  the  eye,  that  we  are  enabled 
to  distinguish  the  forms,  as  well  as  the  colours, 
of  the  things  around  us.  So  you  must  bear  in 
mind,  Kitty,”  he  added,  “ that  the  figures  and  tints 
which  you  see  come  to  your  eye , instead  of  your  eye 
sending  out  anything  to  them;  for,  were  it  other- 
wise, you  would  be  able  to  see  without  any  light 
at  all.” 


I 


V 


THE  WONDEBS  OF  THE  REFRACTION  OF  EIGHT. — Page  871. 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  371 

Humphry  then  applied  himself  to  prove,  experi- 
mentally, that  all  objects  send  off  rays  of  light  of 
the  same  colour  as  themselves. 

Accordingly,  he  took  an  empty  cigar-box,  and 
having  drilled  a fine  pin-hole  at  one  end  of  it,  he 
bored  another  small  hole  in  the  lid — the  latter  being 
for  the  purpose  of  looking  through.  Then,  inside 
the  box,  at  the  end  opposite  the  pin-hole,  he  pasted 
a piece  of  white  paper,  and  placed  a rose-tree  at 
some  short  distance  in  front  of  the  box  itself,  so 
that  the  rays  of  light  from  the  plant  might  pass 
through  the  pin-hole,  and  be  projected  upon  the 
white  paper  at  the  farther  end  of  the  dark  box. 

The  arrangement  being  complete,  he  bade  Kitty 
apply  her  eye  to  the  hole  in  the  lid,  and  tell  him 
what  she  saw. 

“ Dear,  dear !”  cried  the  astonished  girl,  “ I de- 
clare if  there  isn’t  a little  tiny  picture  of  the  rose- 
tree  painted  on  the  paper  inside  the  box.  It  isn’t 
very  plain  though,  Humphry;  but  I can  just  see 
patches  of  red  for  the  roses,  and  patches  of  green 
for  the  leaves.” 

“Yes,”  said  her  brother,  “and  how  could  the 
colours  come  there,  unless  the  plant  itself  was  giv- 
ing off  different  tinted  rays  from  its  leaves  and  flow- 
ers?” 

“ But,  Humphry,”  the  girl  exclaimed,  as  she  con- 
tinued gazing  through  the  hole,  “I  do  believe  it’s 


372 


THE  WONDERS  OF  SCIENCE* 


upside  down ; for  the  patches  of  red  that  I see  are 
below  the  green,  and  in  the  rose-tree  itself  the 
flowers  are  up  above,  and  the  leaves  underneath. 
How  very  strange  !” 

The  lad  having  had  a peep  himself  at  the  image, 
proceeded  to  explain  to  Kitty  the  reason  of  the  pic- 
ture appearing  inverted. 

With  this  view  he  drew  the  annexed  dia- 
gram : 


“ The  rose-bush,”  said  he,  “ is  sending  ofF  rays 
of  light  in  all  directions.  Well,  let  us  suppose  two 
of  these  rays  to  pass  through  the  pin-hole  in  front 
of  the  dark  box,  one  coming  from  the  top,  and 
another  from  the  bottom  of  the  plant.  Now  the 
consequence  would  be,  that  the  two  rays,  on  pass- 
ing through  the  pin-hole,  would  cross  each  other; 
so  that  the  one  which  was  uppermost  would  be 
transferred  to  the  lower  part,  and  that  which  was 
originally  the  bottom  ray  take  the  place  of  the  top 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  373 

one.  Hence  it  is  plain  that  the  image,  or  picture, 
of  the  object  must  appear  upside  down.” 

Kitty  was  perfectly  satisfied  with  the  explana- 
tion, but,  wishing  to  see  the  picture  of  the  rose 
more  plainly  upon  the  paper,  she  asked  Humphry 
whether  he  could  not  admit  more  light  into  the 
box. 

The  brother  smiled  at  the  simplicity  of  the  re- 
quest ; but,  to  let  the  girl  see  the  result  of  enlarg- 
ing the  light-hole,  he  set  to  work  to  make  a greater 
aperture  in  front  of  the  box.  This  done,  he  told 
Kitty  once  more  to  peep  through  the  hole  in  the 
lid. 

“Why,  what’s  the  matter  with  it,  Humphry1?” 
cried  the  sister ; “I  don’t  see  anything  at  all 
now.” 

Humphry  smiled  at  his  sister’s  wonder,  and  pro- 
ceeded to  recount  to  her  the  reason  why  the  picture 
had  become  obliterated.  He  told  her  that  when  the 
hole  was  a very  small  one,  no  two  rays  from  dif- 
ferent parts  of  the  object  fell  upon  the  same  place  ; 
but  that,  now  the  whole  was  enlarged,  the  rays 
that  were  being  sent  olf  in  all  directions  from  every 
part  of  the  rose-tree  became  confused  with  one  an- 
other, so  that  those  from  the  green  leaves  fell  upon 
the  same  part  of  the  paper  as  those  from  the  red 
flowers,  and  the  consequence  was  that  the  one  col- 
our obliterated  the  other. 

For  the  easier  comprehension  of  this  part  of  the 


374  THE  WONDERS  OF  SCIENCE, 

subject,  Humphry  drew  the  subjoined  representa- 
tion of  the  rays  proceeding  from  one  of  the  flowers 


and  one  of  the  leaves ; where  it  will  be  seen  that, 
owing  to  the  enlargement  of  the  aperture  at  the 
front  of  the  box,  the  red  ray  from  the  flower,  and 
the  green  ray  from  the  leaf,  fall  upon  the  same  part 
of  the  paper  at  the  back ; for  as  the  leaf  and  the 
blossom  each  send  off  rays  in  all  directions,  it  is  ev- 
ident that — supposing  only  two  of  these,  for  simplifi- 
cation’ sake,  to  pass  through  the  aperture — one  of 
the  green  leaf-rays  would  fall  upon  the  same  spot 
with  one  of  the  red  blossom-rays,  and  one  of  the  blos- 
som-rays, on  the  other  hand,  become  blended  with 
one  of  the  leaf-rays. 

Kitty  was  not  a little  disappointed  at  the  result 
which  had  followed  the  enlargement  of  the  light- 
hole  ; but  Humphry,  to  console  her,  said  that  it 
was  possible,  by  means  of  a lens,  to  increase  the 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  375 

light,  and  yet  to  prevent  the  rays  from  different 
points  of  the  object  falling  upon  the  same  part  of 
the  paper  at  the  end  of  the  box. 

For  this  purpose  the  lad  placed  a double  con- 
vex lens,  which  he  had  previously  made  out  of  two 
watch-glasses  cemented  together,  into  the  aperture 
at  the  front  of  the  cigar-box,  and  then  told  his 
sister  to  look  once  more  through  the  hole  in  the 
lid. 

Kitty  no  sooner  applied  her  eye  to  the  sight- 
hole  than  she  cried  aloud,  “ O how  beautiful ! I 
declare  it  is  much  brighter  than  the  first,  and  I 
can  now  see  every  leaf  and  blossom  perfectly  made 
out.  It’s  the  picture  of  a little  fairy  rose — that  it 
is.  But  tell  me,  Humphry,”  said  the  girl,  “ how 
could  a little  bit  of  rounded  glass  like  that  which 
you  put  into  the  box  produce  so  wonderful  a 
change  V’ 

“Well,”  returned  the  brother,  “you  recollect  I 
told  you  that  every  object  which  we  see  is  sending 
off  rays  of  light  from  every  part  of  it  in  all  direc- 
tions. In  the  first  case,  when  there  was  a mere 
pin-hole  in  front  of  the  box,  the  aperture  was  so 
small  that  only  one  ray  from  each  point  of  the  rose- 
tree  passed  through  it,  and,  therefore,  the  image 
was  so  dim  you  could  scarcely  make  it  out.  With 
the  convex  lens,  however,  as  many  more  rays  enter 
the  box  from  every  part  of  the  plant,  as  the  lens 
itself  is  bigger  than  the  small  hole  which  we  had 


376 


THE  WONDERS  OF  SCIENCE. 


in  the  box  at  first;  and  the  reason,  again,  why 
these  rays  are  prevented  from  becoming  confused 
one  with  the  other,  and  so  obliterating  the  picture 
- — as  was  the  case  when  we  enlarged  the  light- hole 
in  front  of  the  box,  without  inserting  any  lens  in  it 
— is  because  they  are  all  duly  refracted  by  the  lens, 
so  that  they  severally  fall  in  their  proper  places. 
But  you  will  understand  this  better  by  a drawing.” 
And,  so  saying,  Humphry  prepared  the  illustration 
below  given : 


“ Here  you  see  there  are  three  rays,”  continued 
the  lad,  “ drawn  from  the  top,  bottom,  and  centre 
of  the  object ; three  only  are  given  for  the  sake 
of  simplicity,  though  every  point  of  the  plant  is 
sending  light  from  it  in  the  same  manner  as  here 
indicated.  Well,  Kitty,  the  rays  from  the  flower 
at  the  top  of  the  tree  fall  upon  every  part  of  the 
glass,  and,  by  the  laws  of  refraction,  are  made  to 
come  together  at  a point  on  the  other  side  of  it. 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  377 

Again,  the  rays  from  the  leaves  at  the  bottom  of 
the  tree  fall  upon  every  part  of  the  lens,  and  are  so 
refracted  that  they  all  meet  at  another  point  on  the 
other  side  of  the  glass ; while  those  from  the  rose- 
bud in  the  centre  are  likewise  blended  into  a focus 
at  the  same  distance  behind  the  lens.  But  you 
will  perceive,  that  the  rays  which  come  from  the 
upper  part  of  the  object  fall  at  the  lower  part  of 
the  image ; and  those,  on  the  other  hand,  which 
proceed  from  the  top,  fall  at  the  bottom.  This  is 
because  the  rays  from  these  parts  cross  one  another 
in  the  centre  of  the  lens,  while  those  which  are  sent 
off  from  the  rosebud  in  the  middle  suffer  no  change 
of  position,  because  they  proceed — as  you  observe  by 
the  dotted  lines  in  the  drawing — directly  through 
the  glass,  rather  than  traversing  it  obliquely  as  the 
others  do.” 

“ Oh,  thank  you,  Humphry,”  said  Kitty;  “I  can 
make  it  out  well  now.  The  image  from  the  lens  is 
so- much  brighter  because  it  not  only  allows  more 
light  to  pass  through  the  aperture,  but  prevents  the 
rays  from  the  different  parts  of  the  object  mingling 
one  with  the  other.  But,  Humphry,”  ejaculated 
the  girl,  as  a new  thought  struck  her,  “ the  image, 
as  you  call  it,  is  much  smaller  than  the  rose-tree  it- 
self : why  is  that  V* 

“To  make  you  understand  this,  Kitty,”  answered 
the  boy,  “I  will  place  the  tree  farther  from  the  lens, 
and  you  shall  tell  me  the  effect.” 


378 


THE  WONDERS  OF  SCIENCE. 


Humphry  hud  no  sooner  removed  the  plant  to  a 
greater  distance,  than  the  girl  cried,  “ Oh,  it’s  much 
smaller  than  ever  now!” 

“And  now  that  I bring  it  nearer  the  box,  what 
do  you  see  1”  inquired  the  youth. 

“Why  it  seems  to  grow  and  grow,  Humphry,” 
replied  Kitty,  as  she  continued  peeping  through  the 
hole  in  the  lid,  “ so  that  I fancy  it  would  get  as  big 
as  the  tree  itself.  The  picture,  though,  is  not  near- 
ly so  bright.” 

“No,”  returned  her  brother;  “that  is  because  it 
gets  out  of  focus.  Now  look  you  here,  Kitty ; I 
will  do  another  drawing,  to  enable  you  to  compre- 
hend how  the  size  of  the  image  depends  upon  the  dis- 
tance of  the  object  from  the  lens. 


“ You  must  bear  in  mind,”  proceeded  Humphry, 
on  the  completion  of  the  diagram,  “that  the  rays 
which  pass  through  the  centre  of  a lens  never  change 
their  direction.  Well,  I have  drawn  here,  you 
see,  one  ray  from  the  tip  of  the  arrow,  and  one 
from  the  bottom ; and  as  these  rays  necessarily 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  379 

form  the  extremes  of  the  image,  and  so  regulate  its 
size,  you  will  readily  comprehend  that,  when  the 
object  is,  as  here  represented,  4 yards,  or  feet — or, 
indeed,  4 measures  of  any  kind  — in  front  of  the 
lens,  and  the  image  falls,  also,  at  4 such  measures 
behind  it,  as  at  the  arrow  4,  the  image  itself  must 
be  exactly  of  the  same  size  as  the  object.  If,  how- 
ever, the  image  fell  at  half  the  distance  behind  the 
lens  which  the  object  was  from  the  front  of  it,  then 
the  picture  would  be  only  half  the  size  of  the  body 
producing  it — as  here,  at  the  arrow  2 ; whereas  if 
the  image  was  at  twice  the  distance  of  the  object 
from  the  lens,  as  at  the  arrow  8,  then  it  would  be 
exactly  twice  the  size  of  it.  Consequently,  the  di- 
mensions of  the  image  produced  by  a lens  bear  al- 
ways the  same  proportion  to  the  object  as  the  dis- 
tance of  the  object  from  the  lens  does  to  that  of  the 
image : that  is  to  say,  if  the  object  be  3 times  as  far 
from  the  lens  as  the  image  is,  then  the  image  will 
be  3 times  smaller  than  the  object  itself,  and  vice 
versa,  if  the  object  be  3 times  nearer  the  lens  than 
the  image,  then  the  image  will  be  3 times  larger 
than  the  object.” 

Kitty  having  informed  her  brother  that  she  thor- 
oughly understood  the  matter  now,  Humphry  went 
on  to  tell  her  that,  in  order  to  produce  an  image, 
it  was  necessary  that  the  picture  should  be  received 
upon  some  opaque  or  intransparent  substance,  oth- 
erwise the  rays  of  light  would  pass  through  the  sub- 


380 


THE  WONDERS  OE  SCIENCE. 


stance  itself  without  being  reflected  from,  it  or  sent 
back  to  the  eye. 

“The  opaque  body,”  continued  the  youth,  “upon 
which  the  image  is  thrown,  should  be  of  a white 
colour,  for  this  reflects  the  greatest  amount  of 
light.” 

To  elucidate  this  part  of  the  subject,  Humphry 
removed  the  wooden  end  of  the  cigar-box  that  he 
had  previously  employed,  and  substituted  a piece  of 
ground  glass  in  its  stead;  when  Kitty,  on  placing 
her  eye  behind  the  box,  saw  the  picture  of  the  rose- 
tree  once  more  portrayed  upon  it. 

“ Now,”  added  her  brother,  “if  I smear  the 
ground  glass  over  with  any  grease,  or  even  water, 
so  as  to  increase  its  transparency,  you  will  see  that 
the  image  immediately  disappears.” 

This  done,  Humphry  explained  to  Kitty  that  the 
image  might  be  received  upon  smoke,  or,  indeed, 
any  vapour  that  consisted  of  a number  of  opaque 
white  particles,  and  then  he  recounted  to  her  the 
story  of  the  “spectre  of  the  Brocken.” 

“The  Brocken,”  said  he,  “is  the  name  given  to 
the  loftiest  of  the  Hartz  mountains,  which  is  a pic- 
turesque chain  of  hills  situate  in  the  kingdom  of 
Hanover.  The  highest  of  these  is  elevated  3300 
feet  above  the  sea,  and  commands  the  view  of  a plain 
upwards  of  200  miles  in  extent.  This  spot  has  been 
the  seat  of  the  marvellous  from  the  earliest  periods. 
One  of  the  accounts  given  of  the  4 Spectre  of  the 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  381 

Brocken’  is  that  of  M.  Haue.  After  having  been 
on  the  summit  of  the  mountain  no  less  than  thirty 
times,  he  had,  at  last,  the  good  fortune  of  witness- 
ing the  object  of  his  curiosity.  The  sun  rose  at 
about  4 o’clock  in  the  morning  through  a serene 
atmosphere.  In  the  south-west,  towards  Achter- 
mannshohe,  a brisk  wind  carried  before  it  the 
transparent  vapours  which  had  not  yet  been  con- 
densed into  thick,  heavy  clouds.  About  a quarter 
past  4 M.  Haue  looked  round  to  see  whether  the 
atmosphere  would  afford  him  a free  prospect  to- 
wards the  south-west,  when  he  observed,  at  a very 
great  distance  towards  Achtermannshohe,  a human 
figure,  of  a monstrous  size.  At  this  moment  a 
violent  gust  of  wind  ensued,  and  M.  Haue  sud- 
denly raised  his  hand  to  his  head,  to  prevent  his 
hat  being  carried  away,  when,  to  his  great  aston- 
ishment, he  beheld  the  colossal  figure  in  the  dis- 
tance do  the  same.  He  immediately  made  another 
movement  by  bending  his  body,  and  this  action, 
too,  was  instantly  repeated  by  the  spectral  figure. 
There  was  now  no  doubt  that  what  was  termed  the 
4 Spectre  of  the  Brocken’  was  an  enormous  image 
of  the  spectator  himself  seen  in  the  distance.  M. 
Haue  was  desirous  of  making  other  experiments, 
but  the  figure  disappeared.  He  remained,  how- 
ever, in  the  same  position,  expecting  its  return  ; 
and  in  a few  minutes  it  again  made  its  appearance 
on  the  Achtermannshohe,  when  it  once  more 


382 


THE  WONDERS  OF  SCIENCE. 


mimicked  his  gestures  as  before.  M.  Haue  then 
called  another  person  to  him,  and  having  both 
taken  the  same  position  which  he  himself  had  pre- 
viously occupied,  they  looked  towards  the  Achter- 
mannshohe,  but  saw  nothing.  In  a very  short 
space  of  time,  however,  two  colossal  figures  were 
formed  above  the  eminence,  and,  after  bending 
their  bodies,  and  imitating  the  gestures  of  the  spec- 
tators, they  disappeared.  M.  Haue  and  his  com- 
panion, nevertheless,  retained  their  position,  and 
kept  their  eyes  still  fixed  upon  the  same  spot,  when 
the  two  gigantic  spectres  were  again  beheld  by 
them,  but  this  time  they  were  joined  by  a third, 


and,  strange  to  say,  every  movement  they  made 
was  imitated  by  all  the  three  figures . The  effect, 
however,  varied  in  its  intensity,  being  sometimes 
weak  and  faint,  and  sometimes  strong  and  well- 
defined. 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  383 

“ These  figures  were  merely  shadows  of  the  ob- 
servers, projected  on  dense  vapour,  or  thin  fleecy 
clouds,  which  have  the  power  of  reflecting  much 
light.  They  are  seen  most  frequently  at  sunrise, 
because  at  that  time  the  vapours  and  clouds  nec- 
essary for  their  production  are  usually  generated ; 
and  they  can  be  perceived  only  when  the  sun  is 
throwing  his  beams  horizontally,  because  the  shad- 
ow of  the  observer  would  be  otherwise  projected  up 
in  the  air,  or  down  upon  the  ground.  It  is  very 
probable  that  the  third  figure  observed  by  M.  Haue 
was  formed  by  a duplication  of  one  of  the  others, 
produced  by  unequal  refraction ; though  M.  Haue 
himself  does  not  state  which  of  the  two  figures  was 
doubled.” 

It  may  here  be  added,  that  another  story  of  the 
same  kind  is  told  by  Sir  David  Brewster.  “A 
young  lady  had  ascended  to  the  top  of  the  Mynydd, 
a steep  hill,  about  500  feet  above  the  valley  of  New 
Rednor,  in  South  Wales.  The  sun  was  bright  and 
hot  (it  being  about  2 o’clock  in  the  day).  Having 
picked  some  flowers  on  the  top  of  the  hill,  the  girl 
descended  a little  way,  to  a spot  from  which  she 
could  see  the  road  and  the  carriage  with  her  com- 
panions whom  she  had  left  in  it  below.  After  wav- 
ing the  scarf  which  she  held  in  her  hand  to  her 
friends,  she  suddenly  perceived,  upon  turning  round, 
a figure  standing  a few  yards  from  her  upon  a wet 


384 


THE  WONDERS  OF  SCIENCE. 


spot,  from  which  a little  thin  mist  was  rising.  The  fig- 
ure stood  exactly  facing  her,  and  wavered  a little ; 
but  she  did  not  discover  it  to  be  her  own  image,  till 
she  observed  that,  like  herself,  it  held  a scarf  and  a 
bunch  of  flowers  in  one  hand.  The  dress  and  flow- 
ers were  precisely  similar  to  her  own,  and  the  col- 
ours so  vivid  that  she  could  even  trace  her  own  feat- 
ures in  the  image.  The  effect  was  the  same  as  if 
she  had  been  before  a looking-glass  — when  she 
moved  her  hand,  the  figure  did  the  same.  The  two 
friends  in  the  carriage  saw  the  image  of  the  young 
lady,  and  asked  her,  when  she  joined  them,  what 
companion  she  had  had  on  the  hill.  There  can  be 
no  doubt,”  adds  Sir  David  Brewster,  “that  the  fig- 
ure was  a reflexion  of  the  young  lady,  produced  by 
the  thin  mist  rising  from  the  damp  ground ; for  it 
may  be  proved,  by  experiment,  that  when  the  par- 
ticles of  vapour  are  sufficiently  small,  they  reflect 
light  as  distinctly  as  a surface  of  glass.” 

From  the  production  of  images,  Humphry  passed 
to  the  consideration  of  the  circumstances  by  which 
lenses  appear  to  increase  the  size  of  objects,  and  so  to 
make  them  seem  as  if  brought  nearer  to  us. 

“When  a shilling,”  said  Humphry,  “is  at  the 
distance  of  6 or  8 inches  from  the  eye,  we  can 
read  the  inscription  round  it  with  perfect  distinct- 
ness. At  the  distance  of  3 yards,  however,  we 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  385 


can  no  longer  make  out  the  inscription,  but  see  only 
the  king’s  head  upon  it.  Again,  at  the  distance  of 
only  20  or  30  yards,  we  lose  sight  of  the  head,  and 
can  then  just  distinguish  that  it  is  a round  body; 
whilst,  when  placed  at  about  100  yards  from  us, 
the  coin  is  scarcely  visible.  The  reason  of  this  is, 
that  the  shilling  decreases  in  size  the  farther  it  is 
removed  from  us,  for  we  then  see  it  under  a small- 
er angle , as  it  is  termed  ; and  it  is  found  that  the 
smallest  angle  under  which  an  object  can  be  seen, 
is,  upon  an  average  for  different  sights,  the  60th 
part  of  a degree,  or  one  minute  in  space ; so  that 
when  an  object  is  removed  from  the  eye  about 
3000  times  its  own  diameter,  it  will  only  just  be 
distinguishable.  Consequently,  the  greatest  dis- 
tance at  which  we  can  behold  an  object  like  a shil- 
ling, of  an  inch  in  diameter,  is  3000  inches,  or  250 
feet. 

“Another  drawing,”  added  Humphry,  “will  en- 
able you,  Kitty,  readily  to  comprehend  how  an  ob- 
ject appears  to  diminish  in  size,  according  as  it  be- 


comes more  and  more  distant  from  us,  and  so  gets  to 
be  seen  under  a smaller  angle.” 

Br 


386 


THE  WONDERS  OF  SCIENCE. 


“There,”  continued  the  boy,  “the  first  arrow  is 
seen  under  an  angle  of  120°,*  whereas  the  angle 
under  which  the  second  arrow  is  regarded  is  only 
60°.  Consequently,  though  the  objects  are  the 
same  in  size,  the  one  will  appear  only  4 the  length 
of  the  other.  The  third  arrow,  again,  being  seer? 
under  an  angle  4 times  smaller,  will  seem  to  be 
only  ith  the  size  of  the  first;  whilst  the  fourth 
arrow,  for  the  same  reason,  will  look  as  if  it  were 
only  4th  the  height  of  the  one  next  the  eye ; and 
the  farthest  arrow  of  all  but  x^th  as  large  as  the 
nearest.  Moreover,  if  we  suppose  another  arrow 
still  to  be  so  far  removed  that  the  angle  under  which 
it  is  seen  dwindles  down  to  the  60th  part  of  a de- 
gree,  or  1\  as  it  is  called,  this  will  then  appear  so 
reduced  in  size  as  to  be  only  just  distinguishable 
to  us. 

“Well,  Kitty,”  the  youth  went  on,  “you  now 
understand  that  an  object  appears  to  diminish  in 
size  the  farther  it  is  removed  from  us,  merely  be- 
cause  it  is  seen  under  a lesser  angle;  and,  conse- 
quently, an  object  must  seem  to  us,  on  the  other 
hand,  to  increase  in  size  when  the  image  of  it  is 
brought  nearer  to  the  eye,  and  so  gets  to  be 

* The  range  of  the  eye,  or  diameter  of  the  field  of  vision,  is 
110°  ; consequently,  this  is  the  largest  angle  under  which  an  ob- 
ject can  be  seen.  The  largest  angle,  however,  is  here  made  120°,. 
for  the  simplification  of  the  numbers.  The  range  of  vision  is  frosa 
110°  to  Ih 


/ 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  387 

viewed  under  a greater  angle.  This,  then,  is  all 
that  lenses  really  do  when  they  appear  to  magni- 
fy objects:  that  is  to  say,  they  do  not  absolutely 
increase  the  dimensions  of  the  bodies  under  view, 
but  merely  bring  their  images  nearer  to  the  eye,  and 
so  enable  us  to  see  them  under  a larger  angle. 
lrou  remember  I told  you  that,  with  a shilling,  we 
can  just  see  the  king’s  head  upon  it  at  the  distance 
of  about  10  feet  from  the  eye.  Now,  when  the 
coin  is  at  that  distance,  if  a convex  lens,  having  a 
focus  2\  feet  long,  Jbe  placed  midway  between  the 
shilling  and  the  eye,  the  lens  will,  of  course,  be  5 
feet  from  the  eye  and  5 from  the  shilling ; so  that, 
in  this  case,  it  is  plain,  from  what  I before  ex- 
plained to  you  about  the  size  of  images,*  that  the 
image  of  the  shilling  seen  behind  the  lens  will  be 
exactly  of  the  same  dimensions  as  the  shilling  it- 
self in  front  of  it.  The  object,  therefore,  will  not 
have  been  directly  magnified  by  the  lens.  The  im- 
age, however,  will  be  thus  brought  so  near  to  the 
eye,  that  the  coin  may  be  seen  by  us  at  the  distance 
of  6 inches,  instead  of  10  feet ; and,  consequently, 
being  viewed  under  a proportionately  larger  angle, 
the  shilling  will  seem  to  be  magnified  as  many  times 
as  10  feet  is  greater  than  6 inches;  or,  in  other 
words,  it  will  be  made  to  appear  20  times  larger 
in  our  eyes.  Hence  the  shilling  will  have  been,  ap- 
parently, magnified  20  times,  merely  by  bringing  the 
* See  illustration  at  p.  378, 


388 


THE  WONDERS  OF  SCIENCE. 


image  of  it  20  times  nearer  the  eye — thus.  Where- 
upon the  boy  proceeded  to  delineate  the  following 
diagram ; in  which  the  dotted  lines  from  the  object 


C D 


A represent  the  angle  that  the  shilling  itself  would 
be  viewed  under  without  the  lens,  C,  by  the  eye  at 
B,  while  the  dotted  lines  from  the  image  D show  the 
much  larger  angle  that  such  image  would  be  seen 
under  with  the  lens. 

Humphry  then  prepared  an  experiment  illustra- 
tive of  the  apparent  magnifying  of  objects  by  lenses, 
when  their  images  are  brought  nearer  to  the  eye. 
For  this  purpose  he  got  Kitty  to  bore  a hole  in  the 
shutter  large  enough  to  allow  a lens  to  be  inserted  in 
it.  Then  fixing  the  glass  in  the  aperture,  he  bade  his 
sister  close  the  shutters,  and  place  her  eye  at  about 
2-b  feet  from  the  lens,  for  such  he  knew  to  be  the 
length  of  its  focus. 

“ How  beautiful!”  cried  the  girl,  as  she  gazed 
through  the  transparent  circle.  “I  see  a tiny  im- 
age of  Madern  Church;  and  so  close,  too,  that  I 
could  fancy  it  was  in  the  room  here.” 

“Well,”  said  Humphry,  “the  church  itself,  you 
know,  is  about  1-1-  mile  distant,  or,  let  us  say,  7500 
feet,  and  the  focus  of  the  lens  is  2Jr  feet ; conse- 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  389 

quently  it  follows,  from  what  I have  before  told  you, 
that  the  image  of  the  church  you  see  is  3000  times 
smaller  than  the  church  itself,  for  — 3000. 

Nevertheless,  if  we  could  copy  the  image  of  the 
church  upon  a piece  of  paper — or,  wrhat  would  be 
better  still,  fix  it  upon  a sheet  of  glass,  we  should 
find  that,  on  holding  it  just  as  far  from  the  eye  as  it  is 
now  from  the  lens , the  tiny  image  that  you  now  see 
would  exactly  cover  every  part  of  the  distant  ob- 
ject, and  so  appear  precisely  of  the  same  size  as  the 
church  itself — in  this  manner. 


“Let  us  suppose  the  large  dart,  marked  A here,” 
the  lad  continued,  as  he  drew  the  plan  upon  paper, 
“ to  be  the  height  of  the  church,  and  the  smaller 
dart,  a,  on  the  other  side  of  the  lens,  C,  to  be  the 
size  of  the  image  that  we  see.  Well,  if  you  were 
to  place  your  eye  where  the  lens  now  is,  and  the 
image  just  as  far  in  front  of  the  glass  as  it  now  stands 
behind  it,  it  is  plain,  by  the  dotted  eye  and  arrow  at 
a' , that  the  one  would  exactly  cover  the  other. 

“Hence  it  is  evident,”  added  Humphry,  “that 
the  image  which  you  see  behind  the  lens  is  really 


390 


THE  WONDERS  OF  SCIENCE. 


of  the  same  size  as  the  distant  object  appears  to  be, 
even  though,  as  in  the  case  of  Madern  Church,  the 
image  is  no  less  than  3000  times  smaller  than  the 
object  itself  really  is.  But  when  you  look  through 
a glass,  Kitty,  the  image  of  the  distant  object  is  only 
about  6 inches  from  your  eyes;  so  that,  though  it 
is  of  the  same  size  as  the  object  itself  appears  to  be, 
you  are  viewing  it  at  a shorter  distance  than  the 
length  of  the  focus  of  the  lens ; and,  therefore,  owing 
to  your  regarding  it  under  a greater  angle,  it  seems 
to  be  magnified.  Now,  as  I told  you,  the  focus  of 
the  lens  we  employed  was  2 feet,  or  30  inches 
long ; and,  supposing  your  eye  to  have  been  where 
the  lens  was,  and  the  image  transferred  to  the  other 
side  of  the  lens  (as  indicated  by  the  dotted  eye  and 
arrow  marked  </),  the  image  would  have  seemed 
exactly  the  same  size  as  the  object  itself,  provided 
it  had  been  placed  at  a distance  of  30  inches  in 
front  of  you.  If,  however,  the  image  had  been 
placed  only  6 inches  away  from  your  eye,  it  is  plain 
that  you  would  have  been  viewing  it  5 times  closer 
than  2^  feet,  and  this  would  be  the  same  as  if  the 
dotted  arrow  had  been  shifted  from  a / to  x;  conse- 
quently, it  would  then  have  looked  to  you  5 times 
larger  than  it  really  was,  because  you  were  re- 
garding it  under  an  angle  5 times  greater  than  its 
own. 

“The  result  which  we  come  to  is,  therefore,” 
concluded  the  youth,  “that  the  magnifying  power 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  391 

of  a lens  is  always  equal  to  its  focal  length , divided 
by  the  distance  at  which  the  eye  regards  the  image . 
The  latter,  in  your  case,  Kitty,  was  about  6 inches ; 
so  that  the  lens,  having  its  focus  30  inches  off,  the 
magnifying  power  of  it  is  arrived  at  in  this  man- 
ner: ^0=5.” 

Kitty  asked  whether  it  was  possible  to  magnify 
an  object  any  more  than  that ; when  Humphry 
told  her  that,  had  the  focus  of  the  lens'  he  em- 
ployed been  longer,  its  magnifying  power  would 
have  been  greater;  “ as  for  instance,”  said  he,  “if 
the  length  of  the  focus  had  been  5 feet,  instead 
of  2-lr,  it  would  have  magnified  10  times  instead  of 
only  5,  for  ^^^—10.  So,  again,  had  the  focus 
of  the  lens  been  10  feet,  its  magnifying  power 
would  have  been  doubled  again,  for  1f.in°hea  — 20. 
But,”  continued  the  boy,  “ the  magnifying  power 
might  be  increased  in  another  way — namely,  by 
bringing  the  eye  nearer  to  the  image.  As  yet  we 
have  estimated  the  distance  at  which  the  eye  views 
the  image  produced  by  the  lens  at  6 inches,  be- 
cause that  is  the  length  at  which  we  see  near  ob- 
jects distinctly.  Hold  your  finger  before  your  eye, 
Kitty,  and  you  will  see  that  when  you  bring  it 
very  close  you  can  scarcely  distinguish  it.  With 
a lens,  however,  having  a short  focus,  you  would 
be  able  to  see  the  finger  much  nearer  than  nat- 
urally ; and  then,  for  the  reason  I have  before  given 
you,  it  would  appear  to  be  as  much  magnified  as 


392 


THE  WONDERS  OP  SCIENCE. 


the  distance  at  which  you  beheld  it  distinctly  with 
the  lens  was  less  than  6 inches,  which  is  the  dis- 
tance at  which  you  beheld  it  distinctly  without 
the  lens.  In  my  cupboard  you  will  find  a burn- 
ing-glass, and  that  has  a focus  of  only  2 inches. 
Do  you  get  it,  Kitty,  and  look  at  your  finger 
through  it.” 

The  girl  did  as  she  was  bidden,  and  immediate- 
ly cried,  “ Oh,  Humphry ! what  a horribly  ugly, 
coarse,  thick-looking  thing  it  is ! Why,  I declare 
my  skin  looks  like  an  elephant’s  hide  through  it; 
and  I can  see  every  line  in  it,  like  the  veins  on  a 
leaf!” 

“ Yes,”  returned  her  brother,  “ that  is  because 
you  are  now  looking  at  your  finger  3 times  nearer 
than  you  could  see  it  distinctly  without  the  lens, 
and,  consequently,  you  behold  it  under  a propor- 
tionately larger  angle ; so  that  it  appears  to  you  to 
be  3 times  magnified — for  jj  inc?!es  — 3.  Let  us  then 
apply  the  same  principle  to  the  image  of  Madern 
Church  as  seen  through  the  lens  in  the  shutter, 
and  which,  you  remember,  appeared  to  be  magni- 
fied 5 times,  because  you  saw  it  at  6 inches  from 
your  eye  instead  of  30  inches,  which  was  the  focal 
length  of  the  lens.  But  now,  by  means  of  this 
burning-glass  held  near  your  eye,  do  you  look  at 
the  image  once  more,  and  tell  me,  Kitty,  what  you 
see.” 

The  shutters  were  accordingly  closed  again,  and 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  393 

the  girl  proceeded  to  take  another  peep  at  the  dis- 
tant church  through  the  two  lenses. 

44  Oh,  Humphry !”  she  cried,  44  I see  it  much 
plainer  than  ever;  and  it  is,  as  you  say,  a great 
deal  bigger,  too.” 

44  Of  course  it  is,”  returned  the  brother,  44  for  the 
length  of  the  focus  of  the  burning-glass  is,  as  I 
said,  2 inches ; so  that  you  now  see  the  image  of 
the  church  at  that  distance  from  your  eye,  instead 
of  6 inches,  as  before.  The  image,  therefore,  ap- 
pears to  be  magnified  5 times  by  the  first  lens,  and 
3 times  by  the  second,  or  5x3  = 15  times  in  all; 
and  the  reason  of  its  appearing  to  be  that  number 
of  times  larger  to  you,  is  simply  because  you  are 
looking  at  it  at  15  times  a shorter  distance  than 
the  focal  length  of  the  lens  in  the  shutter,  which  is 
called  the  4 object-glass,’  and  so  seeing  it  by  means 
of  the  other  lens,  which  is  called  the  4 eye-glass,’ 
under  15  times  a greater  angle  than  you  behold  the  ob- 
ject itself  with  your  naked  eye.” 

44 1 understand  it  now  perfectly,  Humphry,  thank 
you,”  said  the  sister,  pleased  with  the  explanation. 
44  And  are  the  telescopes  that  the  sailors  use  made 
upon  the  same  principle'?” 

44  Precisely  so,  Kitty,”  responded  the  brother. 
44  And  in  order  to  find  out  the  magnifying  power 
of  any  of  these,  we  have  merely  to  divide  the  length 
of  the  focus  of  the  object-glass  by  that  of  the  eye- 
glass^ and  the  quotient  will  tell  us  how  many  times 


394 


THE  WONDERS  OF  SCIENCE. 


the  objects  are  enlarged  by  them;  whilst  in  order 
to  make  a telescope  for  ourselves,  we  have  mere- 
ly to  procure  a lens  of  a long  focus — say  12  inch- 
es, and  one  of  a short  focus — say  2 inches,  and 
then  to  set  these  in  a tube  at  the  length  of  the 
two  foci,  or  12  + 2 = 14  inches  apart.  This  tube, 
however,  should  be  a sliding  one,  so  as  to  admit 
of  the  distance  between  the  two  lenses  being  in- 
creased according  as  the  objects  viewed  are  nearer 
at  hand ; for  I told  you  before,  you  remember, 
that  the  nearer  the  object  the  farther  is  the  image 
from  the  lens,  and  vice  versa , the  more  distant 
the  object,  the  shorter  the  focus  of  the  glass  be- 
comes.”* 

* The  arrangement  of  lenses,  above  described,  constitutes  the 
principle  of  what  is  termed  the  “ astronomical  telescope  for  this 
makes  the  objects  appear  upside  down.  Brit,  though  the  inver- 
sion of  a star  or  planet  is  a matter  of  no  moment  in  astronomical 
observation,  such  an  effect  is  most  disagreeable  when  applied  to 
terrestrial  objects.  The  ordinary  telescope  for  land  purposes, 
therefore — or  the  11  day  telescope,”  as  it  is  usually  styled — has 
two  other  lenses  behind  the  eye-lens.  These  lenses  have  both 
the  same  focus  as  the  eye-lens  itself,  and  are  placed  at  a fixed 
distance  from  each  other,  such  distance  being  equal  to  the  sum 
of  their  focal  lengths  : that  is  to  say,  if  the  eye-lens  have  a focus 
of  2 inches,  then  each  of  the  two  other  glasses  should  have  the 
same  length  of  focus,  and  be  placed  at  4 (2+2)  inches  apart  from 
one  another.  The  magnifying  power  of  the  day  telescope  may 
be  calculated  in  the  same  manner  as  that  of  the  astronomical  one 
above  explained  ; for  the  two  additional  lenses  in  the  day  instru- 
ments, having  the  same  focal  length  as  the  eye-lens  itself,  pro- 
duce no  further  enlargement  of  the  objects,  but  serve  only  to  cross 
the  rays  a second  time,  and  so  to  render  the  image  erect  instead 
of  inverted 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  395 

Now  that  Kitty  understood  the  principle  upon 
which  telescopes  were  constructed,  she  begged  her 
brother  to  promise  to  construct  one  as  soon  as  he 
was  well ; and  Humphry  having  consented,  the  two 
then  passed  on  to  the  consideration  of  the  principle 
of  the  microscope . 

“ I have  already  told  you,”  said  Humphry,  on 
entering  upon  the  subject,  “that  the  nearer  an  ob- 
ject comes  to  us,  the  larger  it  appears.  But,  as  you 
saw,  when  you  held  your  finger  close  before  your 
eye,  it  grew  so  indistinct  and  confused,  that  the 
form  of  it  was  almost  as  obscure  as  if  it  had  been 
at  a great  distance  from  you.  Now  this  effect  is 
produced  by  the  greater  divergence  of  the  rays  of 
light,  whenever  an  object  is  brought  nearer  to 
us;  and  when  the  divergence  is  very  great,  the 
crystalline  lens  within  the  eye  has  not  power  to 
collect  the  rays  into  a focus  on  the  retina  at  the 
back  of  the  eyeball.  You  will  understand  how  the 
rays  come  to  diverge  more  and  more  the  nearer  an 
object  approaches  to  us, 
by  the  following  illustra- 
tion. 

“There,  we  will  sup- 
pose the  eye  to  be  looking 
at  some  very  minute  ob- 
ject, like  a speck  of  the  dust  from  a butterfly’s  wing, 
at  the  distance  of  6 inches,  4 inches,  and  2 inches. 
Well,  at  6 inches,  the  rays  of  light  given  off  by  it. 


396 


THE  WONDERS  OF  SCIENCE. 


you  perceive,  diverge  but  slightly  in  comparison 
with  the  angle  at  which  they  enter  the  eye  at  2 
inches.  Consequently,  the  image  produced  within 
the  eye  itself  would,  in  the  latter  case,  be  so  dim 
that  we  should  be  almost  unable  to  distinguish  it. 
In  order,  however,  to  look  at  a very  small  object, 
we  must  bring  it  as  close  as  possible  to  the  eye ; 
so  that,  to  enable  us  to  see  it  distinctly  at  a short 
distance,  we  must  find  out  some  means  of  de- 
creasing the  divergence  of  the  rays  of  light  from 
near  objects  — or,  what  would  be  better  still, 
of  making  the  rays  enter  the  pupil  in  parallel 
lines. 

“ Now  I showed  you,  a short  while  back,  that  a 
convex  lens  causes  the  rays  of  light  from  objects 
placed  in  its  focus  to  pass  out  on  the  other  side  of 
the  glass  parallel  to  each  other.  Consequently  you 
perceive  that,  by  means  of  a double  convex  glass, 
we  can  see  objects  distinctly  when  held  at  i an  inch 
— or  even  the  y^th  of  an  inch — from  our  eye,  pro- 
vided such  be  the  focal  length  of  the  lens  employ- 
ed ; and  thus  we  shall,  for  the  reasons  before  ex- 
plained, obtain  a magnifying  power  which  will  he 
equal  to  the  distance  at  which  the  naked  eye  can 
see  minute  objects  distinctly  divided  by  the  focal 
length  of  the  lens  employed.  For  example,  the  dis- 
tance of  distinct  vision  for  very  minute  objects  may 
be  taken  at  5 inches,  so  that  if  we  make  use  of  a 
lens  having  a focus  of  1 inch,  the  magnifying  power 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  397 

will  be  equal  to  5 inches  divided  by  1 ; that  is  to 
say,  an  object  viewed  with  such  a glass  will  appear 
to  have  its  length  and  breadth  increased  five-fold ; 
so  that  its  length  being  magnified  5 times,  and  its 
hreadtli  5 times  also,  its  entire  surface  will  be  in- 
creased as  much  as  25  times,  or  5x5.  If,  how- 
ever, we  employ  a lens  having  a focus  of  only  -j^j-th 
of  an  inch,  the  linear  magnifying  power  will  be 
equal  to  5 inches  divided  by  yty  (or  that  is 
to  say,  to  50-fold ; while  the  superficial  magnify- 
ing power  will  amount  to  50  x 50,  or  2500-fold ; 
and  if,  again,”  went  on  the  lad,  “ the  lens  employ- 
ed have  a focus  of  only  y-Ljth  of  an  inch,  then  the 
linear  magnifying  power  will  be  equal  to  5 inches 
divided  by  yinjth  (or  — that  is  to  say,  to  500, 

and  the  superficial  magnifying  power  to  500  X 500, 
or  250,000. 

“ A lens  of  a very  short  focus,”  added  Humphry, 
u constitutes  what  is  termed  the  single  microscope. 
For  this  purpose  the  lens  is  usually  made  spherical, 
— as  a sphere,  or  round  ball  of  glass,  has  its  focus 
at  a distance  from  its  centre  equal  to  1-t-  its  own 
radius ; so  that  if  we  had  a small  glass  ball,  of  1 
inch  in  diameter,  the  focus  of  such  a lens  would 
fall  at  -|ths  of  an  inch  from  the  centre  of  the  ball 
itself ; whereas  if  the  ball  was  ith  of  an  inch  in 
diameter,  it  would  have  the  focus  at  T3cths  of  an 
inch  from  its  centre : so  that  you  will  readily  com- 
prehend, Kitty,  how  tiny  a sphere  must  be  used 


398 


THE  WONDERS  OF  SCIENCE. 


in  order  to  give  great  magnifying  power  with  a 
single  microscope.  To  have  a lens  of  -jfyth  of  an 
inch  focus  that  will,  consequently,  be  able  to  mag- 
nify an  object  50  times  in  length  and  breadth, 
it  would  require  the  glass  sphere  to  be  only  about 
TV^ths  of  an  inch  in  diameter.  The  perfect  execu- 
tion of  such  lenses  requires  considerable  skill  in  the 
grinding  and  polishing,  therefore  other  means  of 
constructing  them  have  been  desired.  One  simple 
method  of  forming  a microscopic  lens  consists  in 
drawing  out  (by  means  of  a spirit-lamp)  a thin  strip 
of  window-glass  into  threads,  and  holding  the  end 
of  one  of  such  threads  in  the  flame  until  it  runs 
into  a globule.  The  globule  is  then  cut  otf  and 
set  in  a small  aperture,  in  such  a manner  that  none 
of  the  rays  may  pass  through  that  part  of  the  tiny 
ball  where  it  was  originally  united  to  the  thread. 
Another  process,”  continued  the  youth,  “ consists 
in  taking  up  some  fine-pounded  glass  on  the  wetted 
point  of  a needle,  and  then  melting  it  by  a spirit- 
lamp  into  a globule,  after  which  the  globule  is  re- 
moved, and  once  more  taken  up,  by  the  wetted 
point  of  the  needle,  on  its  round  side,  when  it  is 
again  inserted  in  the  flame,  until  it  becomes  a per- 
fect sphere.  Moreover,  drops  of  water,  as  well  as 
drops  of  oil  or  varnish,  have  been  used  for  micro- 
scopic lenses.  These  are  placed  on  a small  piece 
of  plate  glass,  and  have  considerable  magnifying 
powers.  Further,  the  lenses  from  the  eyes  of  fish 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  399 


have  been  used  for  the  same  purpose  ; but,  in  this 
case,  it  is  necessary  to  look  through  the  lens  in  the 
direction  of  its  axis — or,  in  other  words,  in  the  same 
manner  as  the  fish  did.* 

“ A good  extempore  microscope  may  be  formed  out 
of  two  test-tubes  filled  with  water,  and  placed  one 
across  the  other,  like  the  algebraic  sign  -f-.” 

To  please  his  sister,  Humphry  had  his  spirit-lamp 
lighted,  and  proceeded  to  form  some  little  globules 
of  glass  in  the  flame,  in  the  manner  before  explain- 
ed ; and  then,  having  set  these  upon  a plate  of  brass, 
he  showed  the  delighted  girl  how  wonderfully  ob- 
jects were  magnified  by  them ; and  afterwards  he 
went  on  to  explain  to  her  how  it  was  possible  to 

* Within  the  last  30  years  the  diamond  has  been  used  for 
the  purpose  of  microscopic  lenses  ; for,  owing  to  the  refractive 
power  of  this  precious  stone  being  greater  than  almost  any  other 
known  substance,  and  nearly  double  that  of  glass,  lenses  can  be 
produced  from  it  of  a great  degree  of  magnifying  power,  and  that 
with  a comparatively  small  curvature,  so  that  increased  distinct- 
ness is  obtained  ; while  the  lens  itself,  being  nearly  “ achromatic ,” 
the  image  produced  by  it  is  untinged  by  prismatic  colours.  Mr. 
Pritchard  constructed  the  first  diamond  microscope  in  1826.  The 
diamond  lens  of  this  was  double  convex,  arid  had  a focus  of^th 
of  an  inch,  so  that  its  magnifying  power  wTas  150  times.  Dr. 
Goring,  an  eminent  authority  on  the  subject,  says — “ I conceive 
diamond  lenses  to  constitute  the  ultimatum  of  perfection  in  the 
single  microscope.”  The  sapphire  has  also  been  used  for  the 
construction  of  microscopic  lenses  with  considerable  advantage, 
its  magnifying  power  being  much  greater  than  that  of  glass.  Mr. 
Pritchard  says,  that  the  sapphire,  next  to  the  diamond,  possesses 
all  qualities  requisite  for  the  formation  of  a perfect  magnifier, 
and  presents  less  difficulties  in  the  construction. 


400 


THE  WONDERS  OF  SCIENCE. 


increase  the  microscopic  power  of  lenses,  even  with- 
out diminishing  their  size. 

“ Suppose,”  said  he,  “ that  we  have  a lens  of  \ 
an  inch  focus,  and  which  would,  therefore,  magnify 
the  diameter  of  objects  10  times  ; and  then  suppose 
that,  instead  of  looking  directly  at  the  image,  we 
place  another  lens  of  a short  focus — say  1 inch — 
between  it  and  our  eye,  and  so  view  the  image 
through  the  second  lens.  Well,  this  second  lens 
would,  for  the  reasons  before  given,  magnify  the 
object  5 times  more  ; so  that  it  would  thus  be  made 
to  appear  50  times  bigger  in  all,  the  image  being 
rendered  ten  times  greater  by  the  first  lens,  and  that 
image,  again,  5 times  greater  by  the  second.  This 
constitutes  what  is  termed  the  compound  microscope  ; 
and,  by  means  of  this  instrument,  objects  may  be 
magnified  to  almost  any  extent.” 

Humphry  having  now  thoroughly  made  out  to 
himself,  as  well  as  his  sister,  the  principle  upon 
which  the  power  of  the  microscope  and  telescope  de- 
pends, concluded  the  subject  by  drawing  the  follow- 
ing diagrams,  illustrative  of  the  opposite  action  of 
the  two  instruments : 


Telescopic  arrangement. 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  401 


Microscopic  arrangement. 


“There,”  said  the  boy,  “in  the  one  case,  as  in 
the  preceding  diagram,  the  object  is  at  a considera- 
ble distance  from  the  lens,  and  the  image  near  it; 
while  in  the  other,  as  in  the  above  diagram,  the 
object  is  near  the  lens,  and  the  image  at  a con- 
siderable distance  from  it.  Now  if  we  suppose, 
Kitty,  the  object  to  be  10,000  feet  in  front  of  the 
first  lens,  and  the  image  10  feet  behind  it,  it  fol- 
lows that  the  image,  in  this  case,  would  be  1000 
times  smaller  than  the  object  itself ; and  if  we 
suppose,  on  the  other  hand,  the  object  to  be  y-A-^th 
of  an  inch  in  front  of  the  second  lens,  and  the 
image  to  be  10  inches  behind  it,  then  the  image, 
in  that  case,  would  be  1000  times  larger  than  the 
object  itself.  Let  us  now  imagine  another  lens  to 


Astronomical  Telescope. 


be  placed  before  each  of  the  images — as  here 
shown — so  that  the  eye  may  view  them  at  a 

C c 


402 


THE  WONDERS  OF  SCIENCE. 


shorter  distance  than  it  could  see  them  distinctly 
without  any  such  aid ; and  let  us  say,  again,  that 
the  focal  length  of  this  second  lens  is,  in  both  cases, 
1 inch.  Well,  then,  we  should  be  regarding  the 
image  in  the  upper  diagram  at  a distance  of  1 
inch  instead  of  10  feet,  which  is  the  focal  length 
of  the  object-glass,  and  so  bringing  it  100  times 
nearer  to  our  eye;  the  consequence  would  be,  that 
it  would  appear  to  us  to  be  100  times  larger  than 
it  would  at  the  distance  of  10,000  feet,  so  that 
this  would  be  the  magnifying  power  of  the  instru- 
ment, which,  as  I said  before,  is  always  equal  to 
the  focal  length  of  the  object-glass , divided  by  that  of 
the  eye-glass.  Such,  then,  constitutes  the  arrange- 
ment of  the  astronomical  telescope.  In  the  com- 
pound microscope,  however,”  added  Humphry, 
“ the  magnifying  power  is  estimated  by  multiply- 
ing instead  of  dividing  the  power  of  the  object- 
glass  by  that  of  the  eye-glass;  so  that,  as  we  sup- 
posed the  first  lens  in  the  lower  diagram  to  mag- 
nify the  object  1000  times,  and  the  second  lens 
now  enables  us  to  view  the  image  distinctly 
at  5 times  nearer  the  eye  than  we  could  with- 
out it,  the  gross  magnifying  power,  therefore, 
must  amount  to  no  less  than  1000x5,  or  5000 
times.” 

The  youth  then  went  on  to  explain  to  his  sister 
that  the  same  relation  which  exists  between  the 
telescope  and  the  microscope,  also  holds  good  be- 


THE  WONDERS  OF  THE  REFRACTION  OF  LIGHT.  403 

tween  the  camera-ohscura  and  the  magic-lantern. 
In  the  camera-obscura,  for  instance,  the  object,  as 
in  the  telescope,  is  at  a considerable  distance  in 
front  of  the  object-glass,  and  the  image  at  a short 
distance  behind  it ; whereas  in  the  magic-lantern, 
the  object,  as  in  the  microscope,  is  at  a short  dis- 
tance in  front  of  the  object-glass,  and  the  image 
at  a considerable  distance  behind  it.  In  the  cam- 
era, therefore,  the  image  is  as  much  diminished 
as  it  is  nearer  the  lens  than  the  object ; whilst 
in  the  magic-lantern  the  image  is  as  much  mag- 
nified as  it  is  farther  from  the  lens  than  the  ob- 
ject. 

The  annexed  drawing  will  illustrate  the  action 
of  these  two  instruments  clearer  than  words  can  de- 
scribe them : 


The  reader  has  only  to  suppose  the  image  pro- 


404 


THE  WONDERS  OF  SCIENCE. 


duced  by  the  camera — a portrait,  let  us  say— to  be 
fixed  upon  glass  (by  the  “ collodion  process”  of  pho- 
tography, an  invention  since  Davy’s  time),  and  this 
image  to  be  made  to  serve  as  the  object  (or,  in  plain- 
er language,  the  slide)  of  the  magic-lantern,  in  order 
to  comprehend  how  the  object  in  the  one  instrument 
may  be  made  the  image  in  the  other,  and  vice  versa , 
the  image  of  the  first  the  object  of  the  second. 


CHAPTER  XVI. 


THE  WONDERS  OF  THE  REFLEXION  OF  LIGHT. 

Hitherto  Humphry  had  considered  only  the 
laws  which  regulate  the  transmission  of  light 
through  transparent  bodies.  This  constitutes  the 
branch  of  the  subject  called  dioptrics  (from  dia, 
through,  and  onrofiac , to  see).  The  other  branch, 
termed  catoptrics  (from  Kara,  from,  or  against,  and 
onrofiaL,  to  see),  deals  with  the  laws  of  light  when 
it  is  reflected  or  thrown  back  from  the  surface  of 
any  body  against  which  it  falls.  Accordingly  the 
lad  passed,  in  due  order,  from  the  transmission  to  the 
reflexion  of  the  luminous  rays. 

To  explain  this  part  of  the  subject  the  youth  first 
procured  a piece  of  an  old  looking-glass,  and  having 
got  Kitty  to  close  the  shutters  once  more,  he  placed 
the  looking-glass  upon  the  ground,  so  that  the  ray 


406 


THE  WONDERS  OF  SCIENCE. 


might  fall  just  in  the  middle  of  it;  when,  as  the 
room  was  thoroughly  darkened,  it  was  easy  to  ob- 
serve the  inclination,  or  angle,  at  which  the  light 
fell  on  the  reflector,  as  well  as  to  perceive  the  course 
it  took  afterwards. 

“Why,  I declare,”  cried  Kitty,  as  she  looked  at 
the  bright  streak,  “ it  goes  down  and  then  up 
again ; and  I can  see  the  beam  slanting  away  from 
the  glass  on  each  side,  for  all  the  world  like  a big 
letter  V !” 

“Yes,”  returned  Humphry,  “you  see  the  course 
of  the  beam  is  stopped  by  the  looking-glass,  and 
instead  of  going  through  it,  the  thread  of  light 
that  streams  down  from  the  hole  in  the  shutter  no 
sooner  falls  on  the  mirror  than  it  is  driven  up 
from  it,  precisely  in  the  same  manner  as  if  the  lu- 
minous particles  were  a series  of  hard  balls  project- 
ed against  the  glass,  and  so  made  to  bound  off  from 
its  surface.” 

The  youth  then  called  for  his  arc,  and  proceeded 

to  measure  the  angle  at 
which  the  light  fell  upon 
the  glass,  and  also  the  an- 
. gle  at  which  it  was  reflect- 
ed from  it — thus  : 

“Do  you  see,  Kitty,” 
he  cried,  as  the  eager 
girl  stooped  down  beside  her  brother,  “ the  ray 


THE  WONDERS  OF  THE  REFLEXION  OF  LIGHT.  407 

that  slants  down  from  the  shutter  falls  upon  the 
glass  at  an  angle  of  45°,  and  this  is  what  is  called 
the  angle  of  incidence ; while  the  ray  which  slants 
upwards  from  it  is  reflected  from  the  glass  at  45° 
also,  and  this  is  Wliat  is  called  the  angle  of  re- 
flexion: so  that,  you  perceive,  the  one  is  exactly 
equal  to  the  other , and  this  constitutes  what  is 
termed  the  law  of  reflexion.  For,  no  matter  what 
the  form  of  the  mirror  itself,  or  in  what  direction  a 
ray  of  light  falls  upon  it,  it  is  always  reflected  or 
driven  back  from  the  surface  at  precisely  the  same 
angle  as  it  strikes  upon  it.  As  you  say,  the  two 
rays  form  a kind  of  letter  V,  and  one  prong 
of  the  letter  always  slants  just  as  much  as  the 
other.” 

“ But  suppose  the  surface  of  the  glass,  Humphry, 
was  to  be  hollowed  out  like  a bowl,  would  it  do  so 
then  ?”  inquired  the  girl. 

“Certainly,”  was  the  reply;  “and  if  the  rays 
falling  upon  it  then  were  parallel  one  to  the  other, 
you  would  find,  upon  drawing  the  figure  on  paper, 
that  they  would  all  meet  together  at  one  point  in 
front  of  the  glass,  which  would,  consequently,  be 
the  focus — the  distance  of  such  focus  being  equal  to 
half,  the  radius , or  semi-diameter , of  the  curvature 
of  the  mirror  itself  Give  me  the  compasses  and 
open  the  shutters,  Kitty,  and  you  shall  soon  see 
what  I mean.” 


408 


THE  WONDERS  OF  SCIENCE. 


In  a few  minutes  the  following  diagram  was  de- 
scribed : 


Convex  Mirror. 


Concave  Mirror. 


\ 


\ 


u There!”  cried  Humphry,  as  he  put  the  last 
touch  to  the  drawing,  “ the  two  curved  lines  repre- 
sent the  surfaces  of  a convex  and  a concave  mirror, 
the  curvatures  of  which  form  portions  of  a circle, 
having  its  centre  at  the  point  where  the  unbro- 
ken lines  meet.  Now,  these  unbroken  lines,  being 
drawn  in  each  case  from  the  centre  to  the  surface 
of  the  mirror  itself,  are  exactly  perpendicular  to 
the  points  where  the  rays  of  light  fall ; and  if  you 
measure  with  the  arc  the  angle  which  the  dotted 
parallel  lines  form  on  one  side  of  the  unbroken 
ones,  you  will  find  that  they  are,  in  every  case, 
here  equal  to  that  which  the  dotted  slanting  lines 
form  on  the  other  side  of  the  same  perpendicular. 
Consequently,  you  perceive  that,  by  a concave 


TTIE  WONDERS  OF  THE  REFLEXION  OF  LIGHT.  409 

mirror,  the  rays  are  made  to  converge  to  a focus  in 
front  of  the  mirror  itself;  whereas  by  a convex 
mirror  the  rays  are  made  to  diverge , as  if  they 
came  from  a focus  behind  the  mirror  itself.  Now 

"V 

this,  you  remember,  is  precisely  the  same  as  what 
takes  place  with  concave  and  convex  lenses ; for  a 
concave  lens  has  its  focus  in  front  of  it,  like  a 
concave  mirror,  but,  owing  to  the  rays  passing 
through  the  lens  in  the  one  case,  and  being  driven 
back  from  the  mirror  in  the  other,  they  are  made 
by  the  lens  to  diverge  and  by  the  mirror  to  con- 
verge. So  that,  while  the  concave  lens  diminishes 
the  apparent  size  of  objects,  the  concave  mirror 
magnifies  them.  The  same  thing  holds  good,”  con- 
tinued the  boy,  “ with  a convex  lens  and  a convex 
mirror ; they  both  have  their  focus  behind  them, 
but  the  rays,  in  passing  through  the  lens,  converge 
to  a point,  whereas,  being  driven  back  from  the 
mirror,  they  diverge  ; and  so,  while  the  convex  lens 
magnifies , the  mirror  diminishes  the  apparent  size  of 
objects.” 

Next,  Humphry  directed  his  sister  to  place  her- 
self alongside  the  looking-glass  over  the  mantel- 
piece, while  he  did  the  same  facing  her,  and  in 
such  a manner  that  neither  could  see  their  own 
figure  reflected  in  the  mirror.  It  would  then  be 
found,  he  said,  that  they  would  each  behold  the 
other,  and  at  exactly  the  same  distance  behind  the 
glass  as  they  were  in  front  of  it.  Tn  this  manner : 


410 


THE  WONDERS  OF  SCIENCE. 


aNow  the  reason  why  I see  you,”  said  the  lad, 
“ and  you  see  me  in  another  place  than  we  really  oc- 
cupy, is,  because  the  rays  reflected  by  the  glass  enter 
our  eyes  in  that  direction ; and,  as  I told  you  be- 
fore, an  object  is  always  seen  by  us  in  the  direction 
which  the  ray  has  at  the  moment  of  reaching  the 
eye , without  regard  to  what  may  have  been  its  course 
previously.  Your  image,  of  course,  Kitty,  is  on 
the  surface  of  the  glass  itself,  and  not  behind  it, 
as  it  appears  to  you  to  be ; and  what,  I dare  say, 
will  sound  stranger  to  you,  is,  that  the  image  itself 
upon  the  glass  is  exactly  half  the  size  that  it  seems 
to  be  behind  it : for  since,  when  you  look  at  your- 
self in  the  glass,  your  image  appears  to  be  just  as 
far  at  the  back  as  you  are  standing  in  front  of  the 


THE  WONDERS  OF  THE  REFLEXION  OF  LIGHT.  411 

mirror,  it  is  evident  that  the  mirror  itself  must  be 
half-way  between  you  and  your  apparent  image ; 
so  that  it  will  cut  in  half  the  cone  of  rays  which 
enter  your  eye  from  the  surface  of  the  looking- 

glass. 

>-• — w 

i 

* S'T~  V\ 

• 'f 

} y . dSf  { 

y 

\'\V* 

t 

“ There  is  a picture,”  continued  Humphry,  as  he 
put  the  drawing  before  his  sister,  “of  a person 
looking  at  himself  in  the  glass ; and  you  will  see, 
by  the  rays  from  his  chin  and  forehead,  which  are 
reflected  in  a point  to  the  eye,  that  a vertical  line 
A . . . B,  at  the  surface  of  the  glass,  must  be  exactly 
equal  to  half  the  length  of  the  image,  since  the  image 
and  the  eye  of  the  spectator  are  always  at  equal  dis- 
tances from  the  glass  itself.  But  the  image,  which 
appears  to  be  behind  the  glass,  is  seen  under  the 
same  angle  as  the  image,  which  is  really  on  the  sur- 
face of  it ; and  so,  for  the  reasons  I before  gave  you, 
when  speaking  of  the  apparent  size  of  objects  in 
general,  the  one  behind  the  glass  appearing  to  be 
at  twice  the  distance  of  the  other,  naturally  seems 
to  be  twice  as  large  as  the  image  on  the  surface 
really  is. 


412 


TIIE  WONDERS  OF  SCIENCE. 


“ I have  already  shown  you,  Kitty,”  went  on  the 
youth,  after  a pause,  “ that  if  two  persons  stand  in 
front  of  a mirror,  and  each  at  opposite  sides  to  it, 
they  will  see  one  another,  but  not  themselves ; and 
this  constitutes  the  principle  of  what  is  termed  the 


magician  s mirror. 

“ Here  is  a plan,”  said, 
Humphry,  “of  the  ordi- 
nary arrangement.  The 
black  lines  we  will  suppose  to  represent  the  walls  of 
two  adjoining  apartments.  At  the  end  of  each  of 
the  rooms  there  is  an  aperture,  made  large  enough 
to  place  behind  it  a looking-glass  that  is  capable  of 
reflecting  the  whole  figure.  In  each  of  these  aper- 
tures there  is  inserted  a sheet  of  plate-glass,  which 
is  surrounded  with  a gilt  frame,  so  as  to  have  the 
appearance  of  an  ordinary  mirror ; and  behind  this 
a real  looking-glass  is  placed,  slanting  at  an  angle 
of  45°,  and  so  large,  that  a person  looking  into  the 
sheet  of  plate-glass  cannot  see  the  edges  of  the 
slanting  mirror  behind  it.  With  such  an  arrange- 
ment, it  is  plain  that  a person  looking  into  either 
of  the  mirrors  will  not  see  himself,  but  any  one 
who  may  chance  to  be  looking  at  the  same  time 
into  the  mirror  in  the  adjoining  room.  Conse- 
quently, on  looking  into  the  mirror  and  believing 
that  he  should  see  his  own  figure  reflected  in  it  as  in 
an  ordinary  looking  glass,  his  astonishment  will  be 
great  in  beholding  himself  transformed  into  another 


THE  WONDERS  OF  THE  REFLEXION  OF  LIGHT.  413 

person,  or,  indeed,  into  some  living  animal  that  may 
be  placed  in  front  of  the  neighbouring  glass.” 

Kitty  observed  to  her  brother,  that  she  remem- 
bered having  seen  the  same  kind  of  an  apparatus  in 
a booth  in  a fair ; and  by  it  persons  were  said  to  be 
shown  their  future  lovers. 

Humphry  told  her  that  it  was  by  the  same  means 
that  people  were  made  to  see,  apparently,  through 
paving-stones. 

“For  if,”  said  the  boy,  “by  the  arrangement  I 
have  explained  to  you,  it  is  possible  to  see  a figure 
in  another  apartment — a brick  wall  intervening — it 
is  obvious  that,  by  the  same  device,  an  object  placed 
on  one  side  of  a paving-stone  could  be  readily  seen 
on  the  other. 

“But  the  concave  mirror,”  continued  Humphry, 
“ is  capable  of  producing  far  more  wonderful  effects, 
for  the  image  from  this  appears  suspended  in  the  air ; 
so  that  if  the  mirror  and  the  object  are  hidden  from 
view,  the  effect  is  almost  supernatural.  This  illus- 
tration represents  the  arrangement  usually  employed 
in  such  cases — 


414 


THE  WONDERS  OF  SCIENCE. 


“ Here  you  perceive,  Kitty,”  added  the  lad,  u the 
two  sides  of  a room,  at  the  end  of  which  there  is  a 
square  opening,  with  a picture-frame  surrounding 
it.  Outside  the  room,  in  an  adjoining  apartment, 
is  placed  a large  concave  mirror ; and  so  arranged, 
that  when  an  object  is  set  a little  above  the  floor  in 
front  of  it,  a distinct  image  of  it  may  be  formed  in 
the  centre  of  the  aperture  at  the  end  of  the  room, 
where  the  spectators  are  assembled.  Now,  if  the 
opening  be  filled  with  smoke,  that  is  made  to  rise 
in  clouds  from  a chafing-dish  concealed  outside,  the 
image  of  any  object  placed  in  the  one  focus  of  the 
mirror  in  the  adjoining  apartment  will  appear  in 
the  other  focus  at  the  centre  of  the  frame,  and  seem 
to  be  depicted  on  the  clouds  of  smoke  there  as  a 
back-ground.  It  is  a favourite  experiment  to  place 
a skull,  strongly  illuminated,  in  the  outer  apart- 
ment, and  to  reflect  an  image  of  it  amid  the  smoke, 
so  as  to  be  visible  to  the  spectators  in  the  inner  room. 
The  trick  of  the  mysterious  dagger,  too,  is  very 
popular.  The  ordinary  way  of  performing  this  is  by 
placing  a basket  of  fruit  in  the  one  focus  of  the  mir- 
ror, so  that  a distinct  aerial  image  may  be  formed 
of  it  in  the  frame.  One  of  the  spectators  is  then 
desired  to  take  some  fruit  from  the  basket ; and  as 
he  approaches  for  that  purpose,  a person,  prop- 
erly concealed,  withdraws  the  real  basket  of  fruit 
with  one  hand,  and  with  the  other  substitutes  a 
dagger,  the  image  of  which  seems  to  strike  at  the 


THE  WONDERS  OF  THE  REFLEXION  OF  LIGHT.  415 

body  of  the  spectator,  and  the  thrust  of  the  bright 
polished  steel  at  his  breast  never  fails  to  produce 
a powerful  impression.  Now,  it  can  scarcely  be 
doubted  that  a concave  mirror  was  the  principal 
instrument  by  which  the  heathen  gods  were  made 
to  appear  in  the  ancient  temples.  Jamblichus  in- 
forms us,  that  the  ancient  magicians  made  the  gods 
visible  to  the  people  among  clouds  of  incense.  And 
in  the  middle  ages  the  Pontiff,  Theodore  Santa- 
baren,  who  was  celebrated  for  his  power  in  work- 
ing miracles,  exhibited  to  the  Emperor  Basil  of 
Macedonia  the  image  of  his  lost  son,  magnificently 
dressed,  and  mounted  on  a superb  charger.  The 
apparition  of  the  youth  seemed  to  rush  towards  his 
father;  and,  throwing  himself  into  his  arms,  van- 
ished. This  effect  was  doubtlessly  produced  by 
reflecting  the  image  of  a picture  of  the  emperor’s 
son  on  horseback;  and  the  picture  being  brought 
nearer  to  the  mirror,  the  image,  of  course,  ap- 
peared to  advance  until  it  reached  the  emperor’s 
arms,  where  it  naturally  eluded  his  grasp.  The 
celebrated  Benvenuto  Cellini  has  left  us  an  account 
of  a more  modern  necromancy,  in  which  he  him- 
self took  a part,  in  the  middle  of  the  sixteenth  cen- 
tury. 

“ ‘It  happens,’  says  Cellini,  proceeded  Humphry, 
as  he  read  the  account  to  his  sister,  ‘through  a 
variety  of  odd  accidents,  that  I made  acquaintance 


416 


THE  WONDERS  OF  SCIENCE. 


with  a Sicilian  priest,  who  was  a man  of  genius, 
and  well  versed  in  the  Latin  and  Greek  authors. 
Chancing  one  day  to  have  some  conversation  with 
him,  when  the  subject  turned  upon  the  art  of  nec- 
romancy, I,  who  had  a great  desire  to  know  some- 
thing of  the  matter,  told  him  that  I had  all  my 
life  felt  a curiosity  to  be  acquainted  with  the  mys- 
teries of  the  art.  The  priest  made  answer,  that  the 
man  must  be  of  a resolute  and  steady  temper  who 
enters  upon  that  study.  I replied,  that  I had  forti- 
tude and  resolution  enough,  if  I could  but  find  an 
opportunity.  The  priest  subjoined,  ‘If  you  think 
you  have  the  heart  to  venture,  I will  give  you  all 
the  satisfaction  you  can  desire.’  Thus  we  agreed  to 
enter  upon  a plan  of  necromancy.  The  priest,  one 
evening,  prepared  to  satisfy  me,  and  desired  me  to 
look  out  for  a companion  or  two.  I invited  one 
Vincenzio  Romoli,  who  was  my  intimate  acquaint- 
ance; and  he  brought  another  with  him.  We  re- 
paired to  the  Coliseum;  and  the  priest,  according 
to  the  custom  of  necromancers,  began  to  draw  cir- 
cles upon  the  ground,  with  the  most  impressive  cer- 
emonies imaginable.  He  likewise  brought  hither 
asafoetida,  several  precious  perfumes  and  fire,  with 
some  compositions  also,  which  diffused  noisome  va- 
pours. As  soon  as  he  was  in  readiness,  he  made  an 
opening  to  the  circle ; and  having  taken  us  by  the 
hand,  ordered  the  other  necromancer,  his  partner,  to 


THE  WONDERS  OF  THE  REFLEXION  OF  LIGHT.  417 

throw  the  perfumes  into  the  fire  at  a proper  time, 
entrusting  the  care  of  the  fire  and  the  perfumes  to 
the  rest ; and  thus  he  began  his  incantations.  This 
ceremony  lasted  above  an  hour  and  a half,  when 
there  appeared  several  legions  of  devils,  insomuch 
that  the  amphitheatre  was  quite  filled  with  them.’ 
Cellini  afterwards  tells  us,  ‘that  the  necromancer 
called  by  their  names  a multitude  of  demons,  who 
were  the  leaders  of  the  several  legions,  and  ques- 
tioned them  by  the  power  of  the  eternal,  uncreated 
God,  who  lives  for  ever,  in  the  Hebrew  language, 
and  likewise  in  Latin  and  Greek,  and  then  the 
amphitheatre  was  almost  in  an  instant  filled  with 
demons,  more  numerous  than  at  the  former  conju- 
ration. The  necromancer  requested  me  to  stand 
resolutely  by  him,  because  the  legions  were  now 
above  a thousand  more  in  number  than  he  had  de- 
signed ; and,  besides,  these  were  the  most  danger- 
ous. The  boy  who  had  accompanied  us  was  in  a 
terrible  fright,  saying  that  there  were  in  that  place 
a million  of  fierce  men,  who  threatened  to  destroy 
us ; and  that,  moreover,  four  armed  giants  of  enor- 
mous stature  were  endeavouring  to  break  into  our 
circle.  Vincenzio  Romoli  quivered  like  an  aspen 
leaf.  Though  T was  as  much  terrified  as  any,  I did 
my  utmost  to  conceal  the  terror  I felt ; so  that  I 
greatly  contributed  to  inspire  the  rest  with  resolu- 
tion. But  the  truth  is,  I inwardly  gave  myself  over 

D D 


418 


THE  WONDERS  OF  SCIENCE. 


as  a dead  man.  The  boy  placed  his  head  between 
his  knees,  and  said,  ‘In  this  posture  will  I die,  for 
we  shall  all  surely  perish.’  In  this  condition,  con- 
cludes Benvenuto,  we  stayed  till  the  bell  rang  for 
morning  prayers.’  " 


CHAPTER  XVII. 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY. 

The  young  philosopher  had  now  completed  his  in- 
vestigations concerning  the  refraction  and  reflexion 
of  light.  He  had  ascertained — 

1.  That  all  substances  in  nature  are  divisible 
into  two  classes,  viz.  luminous  and  non-luminous 
bodies. 

2.  That  luminous  bodies  send  off  rays  of  light 
from  them  in  all  directions , and  that-  such  rays  pro- 
ceed in  straight  lines  while  traversing  the  same  me- 
dium. 

3.  That  non-luminous  bodies  are  transparent , or 
opaque  ; that  is  to  say,  they  either  allow  the  rays  of 
light  emitted  by  luminous  bodies  to  pass  through 
them,  or  else  they  arrest  their  progress ; sometimes, 
in  the  latter  case,  driving  them  off  from  their  sur- 
faces, and  sometimes  absorbing  them. 

4.  That  when  a ray  of  light  falls  obliquely  on  a 
transparent  body  it  is,  on  entering  it,  refracted  or 


420 


THE  WONDERS  OF  SCIENCE. 


bent,  in  a greater  or  less  degree,  out  of  its  previous 
straight  course. 

5.  That  when  a ray  of  light  is  driven  off  or  re- 
flected from  opaque  (or  even  transparent)  bodies,  the 
angle  of  reflexion  is  invariably  equal  to  the  angle  at 
which  the  ray  falls  upon  their  surfaces. 

As  yet,  however,  Humphry  had  dealt  only  with 
white  or  ordinary  uncoloured  light,  and  he  was  now 
about  to  study  the  phenomena  of  colour  itself — to 
investigate  the  laws  which  regulate  the  production 
of  the  varied  tints  on  the  earth,  and  to  ascertain,  if 
possible,  the  means  by  which  the  soil  is  painted  with 
a thousand  hues,  and  how  the  colourless  sunbeam 
becomes  broken  up  into  countless  dyes  as  it  falls 
upon  the  flowers  and  the  rocks,  and  is  driven  back 
by  them  to  the  eye,  arrayed  in  all  the  charm  of  va- 
riegated lustre. 

“ How  comes  it,”  said  Humphry  to  himself,  as  he 
thought  over  the  subject,  “ that  the  earth  by  night 
is  black  and  sombre,  as  if  a pall  were  spread  over 
the  dead  globe — that  the  trees  have  then  a dim, 
spectral  look — that  the  sky  is  dusky  as  a canopy 
of  smoke,  and  that  the  buildings  seem  like  masses 
of  dense  shadow  darkening  the  air,  so  that  the  world 
about  us  is  as  colourless  as  a cavern,  and  the  beauty 
of  surrounding  nature  blotted  out  with  the  universal 
gloom  ? And  how  is  it,  too,”  mused  the  poetic  boy, 
u that  the  beams  of  the  returning  sun  have  power 
to  dye  the  fields  and  sky  with  the  richest  hues — to 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY.  421 


crimson  the  clouds  with  the  glowing  tints  of  dawn, 
and  to  revive,  as  it  were,  in  an  instant,  the  infinite 
colours  of  the  flowers,  so  that  the  ground  grows 
suddenly  iridescent  with  their  various  dyes  *?  How 
comes  it,  again,  that  at  the  tropics,  where  the  sun 
steeps  the  earth  in  a flood  of  light,  the  plumage 
of  the  birds  and  the  blossoms  of  the  plants  are  un- 
rivalled for  the  gorgeousness  of  their  colours;  and 
that  as  we  proceed  thence  to  colder  climates  we 
find  a regularly  declining  chromatic  scale,  the  tints 
becoming  less  and  less  vivid  till  we  reach  the  Poles, 
where  Nature  is  arrayed  in  one  unvarying  robe  of 
white1?” 

But  Humphry  was  too  anxious  to  experiment 
to  continue  dreaming  over  the  matter,  and,  accord- 
ingly, he  got  his  sister  to  darken  the  room  once 
more,  and  then  attaching  a prism  in  front  of  the 
hole  in  the  shutter,  he  proceeded  to  throw  the 
spectrum  on  the  wall  in  the  manner  before  de- 
scribed. 

Kitty  was  as  delighted  as  the  boy  with  the 
beauty  of  the  image,  nor  could  she  help  wonder- 
ing how  it  happened  that  a simple  stick  of  white 
glass  could  resolve  the  sunbeam  into  such  exquisite 
tints. 

Humphry  told  her  that  the  image  she  saw  on  the 
wall  was  merely  an  oblong  picture  of  the  sun  itself, 
the  orb  being  drawn  out  to  that  figure  by  the  refrac- 
tion of  the  glass.  The  vividness  of  the  colours  de- 


422 


THE  WONDERS  OF  SCIENCE. 


pends  upon  the  smallness  of  the  aperture  through, 
which  the  light  is  admitted,  and  the  distance  of 
the  screen  upon  which  the  spectrum  is  made  to 
fall ; so  that  if  the  hole  in  the  shutter  were  small- 
er, and  the  wall  farther  off,  the  spectrum  would  be 
much  brighter.  The  colours,  he  added,  came  from 
the  decomposition  of  the  sunbeam  into  its  elementa- 
ry tints. 

“You,  doubtless,  Kitty,  think  the  light  of  the 
sun  to  be  simple  and  uncompounded,  and  little 
dream  that  every  ray  of  white  light  which  meets 
your  eye  is  made  up  of  seven  other  beams,  and 
each  coloured  with  some  one  of  the  tints  you  see 
in  the  spectrum  here ; and  it  is  solely  because  the 
sunbeam  is  a compound  rather  than  a simple  thing, 
and  that  each  of  the  seven  rays  of  which  it  is  com- 
posed have  different  properties  and  refrangibilities, 
that  this  glass  prism  has  the  power  of  separating 
them  one  from  the  other,  and  so  of  resolving  the 
compound  beam  into  its  seven  elementary  rays. 
Look  here,”  he  continued ; “ were  it  not  for  this 
prism  the  beam  which  comes  through  the  hole  in 
the  shutter  would  proceed  in  its  previous  course, 
and  strike  upon  the  floor;  but  by  means  of  this 
instrument  it  is  refracted , or  bent  out  of  its  path, 
and  as  the  coloured  beams  of  which  it  is  composed 
are,  as  I said,  all  differently  refrangible,  the  red 
ray  here,  being  the  least  refrangible  of  all,  is  the 
least  bent  out  of  its  course,  and  so  made  to  appear 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAHPY.  423 

at  the  bottom  of  the  spectrum  ; whereas  the  violet 
ray,  which  is  the  most  refrangible,  undergoes  the 
most  deviation,  and  thus  is  found  at  the  upper  part 
of  the  coloured  image.” 

Kitty  acknowledged  that  it  was  beyond  her  pow- 
er to  comprehend  how  a beam  of  white  light,  which 
appeared  to  her  to  be  devoid  of  all  colour  whatever, 
could  be  really  composed  of  every  kind  of  colour. 
“ How  was  it  possible,”  she  said,  “ for  violet,  and 
blue,  and  green,  and  yellow,  and  red,  when  mixed 
together,  to  form  white?” 

Humphry  smiled  at  his  sister’s  incredulity,  and 
said  he  would  show  her  that  it  was  quite  possible  to 
put  the  parts  of  the  sunbeam  together  again — for 
by  the  same  means  as  he  had  decomposed  the  white 
beam  into  its  seven  coloured  rays,  so  would  he  com- 
pound those  seven  coloured  rays  again  into  one  col- 
ourless beam. 

The  girl  was  all  eagerness  to  see  the  composite 
nature  of  light  thus  practically  demonstrated,  and  in 
obedience  to  her  brother’s  instructions  she  proceeded 
to  place  a sheet  of  white  pasteboard  against  the  wall, 
so  that  the  spectrum  might  fall  upon  it,  and  then 
to  bring  it  gradually  nearer  the  prism. 

As  Kitty  did  this,  she  noticed  that  the  spectrum 
grew  smaller  and  dimmer ; but  though  the  colours 
began  to  mix  and  encroach  upon  one  another  as 
she  advanced  towards  the  prism,  she  found  that, 
even  when  the  pasteboard  screen  was  brought  close 


424 


THE  AVONDEES  OF  SCIENCE, 


to  the  face  of  the  glass  she  could  still  recognise  the 
separation  of  the  light  into  its  elementary  coloured 
beams. 

This  done,  Humphry  proceeded  to  annex  to  the 
prism  already  employed  another,  which  was  exactly 
similar  in  all  respects — being  made  of  the  like  kind 
of  glass,  and  having  a like  refracting  angle — to  the 
previous  one.  The  second  prism,  however,  was 
placed  in  the  opposite  direction  to  the  first,  so  that 
while  the  base  of  the  one  was  uppermost,  that  of  the 
other  was  underneath — -as  here  shown : 


The  reason  of  this  arrangement  was,  as  Humphry 
explained,  that  the  second  prism  might  exactly  undo 
what  the  first  had  previously  done,  so  that  the  rays 
being  now  refracted  by  the  one  in  an  opposite  direc- 
tion to  the  other,  they  would  be  all  brought  together 
again,  and  made  to  strike  upon  the  same  spot  as  they 
would  have  fallen  upon  had  no  such  instruments 
been  interposed. 

The  apparatus  being  fixed,  the  ray  from  the  hole 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY.  425 

in  the  window-shutter  no  sooner  passed  through  the 
two  prisms  than  the  coloured  spectrum  which  the 
beam  had  been  previously  resolved  into  vanished 
from  the  wall,  and  a round  white  spot  of  light  ap- 
peared upon  the  floor. 

Kitty  was  so  wonder-stricken  at  what  she  saw, 
that  she  looked  at  Humphry  with  the  same  fixed 
stare  as  a child  gazes  at  some  parlour  magician. 

“You  see,  then,  sister,”  said  the  lad,  “that  seven 
coloured  rays  may  be  compounded  again  into  one 
white  one,  even  as  one  white  beam  can  be  decom- 
pounded into  seven  coloured  ones.  So  that,  incred- 
ible as  it  may  seem  to  you,  it  is  impossible  to  avoid 
the  conclusion  that  white  light  is  a composite  thing, 
and  made  up  of  a number  of  other  kinds  of  light 
that  are  widely  different  from  it.  But,”  continued 
Humphry,  “ there  is  another  and  simpler  means  of 
proving  this  point  to  you.” 

For  this  purpose  the  girl  had  to  procure  from  the 
colour-shop  seven  different  colours  in  powder,  each 
of  the  same  tint  as  one  of  the  rays  in  the  spectrum. 
These  were  afterwards  mixed  in  the  same  proportion 
as  the  rays  themselves  bore  to  one  another,  and,  to 
Kitty’s  astonishment,  the  result  was  a kind  of  grey- 
ish white , produced  by  the  mingling  of  the  whole ; 
and  Humphry  told  her  that,  were  it  possible  to  ob- 
tain colours  of  precisely  the  same  tint  as  those  in 
the  spectrum,  a perfect  white  would  be  the  conse- 
quence. 


426 


THE  WONDERS  OF  SCIENCE.. 


“Again,”  the  youth  continued,  “if  we  take  a cir- 
cle, and  paint  round  it  the  several  prismatic  tints 
in  the  same  proportion  as  they  exist  in  the  spec- 
trum itself,  and  cause  these  to  revolve  so  rap- 
idly that  the  eye  is  unable  to  see  any  one  of  them , 
but  rather  perceives  the  whole  at  once,  the  paper 
will  no  longer  appear  coloured  like  the  rainbow  to 
us,  but  seem  really  white  as  it  flashes  past  the 
eye.” 

It  was  necessary,  however,  before  doing  this,  to 
measure  the  several  lengths  of  the  coloured  spaces  in 
the  spectrum  itself,  when  it  was  found  that  the  vari- 
ous prismatic  tints  were  in  the  proportions  hereun- 
der given : 


Proportionate  Width  of  the 
Bands  of  Colours. 

Violet  80 

Indigo  48 

Blue  60 

Green  60 

Yellow  40 

Orange  27 

Red  45 

360 


. Greatest  Chemical  Action. 


. . Greatest  Light. 


. . Greatest  Heat. 


The  next  step  was  to  colour  a circular  piece  of 
paper,  as  nearly  as  possible  in  the  same  manner  as 
the  spectrum,  and  this  was  done  after  the  following 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY.  427 

fashion — where  it  will  be  seen  that  the  outer  colour- 
ed circle  is  nothing  more  than  the  prismatic  spec- 
trum bent  round  till  its  two  ends  meet  at  the  point 
between  the  violet  and  red — the  entire  circle  itself 
being  supposed  to  be  divided  into  360  parts. 


The  circular  spectrum,  when  finished,  was  placed 
upon  a humming-top,  and  the  top  being  made  to 
spin  as  rapidly  as  possible,  the  prismatic  disc,  as  it 
whirled  past  the  eye,  appeared  to  be  absolutely  col- 
ourless ; for  each  tint  as  it  revolved  left  its  impres- 
sion upon  the  retina  but  for  an  instant,  and  this  be- 
ing immediately  afterwards  covered  by  the  tint  which 
was  next  to  it,  the  result  naturally  was,  that  the 
whole  of  the  seven  colours  fell  upon  precisely  the 
same  part  of  the  retina  itself,  and  so  produced  a 
composite  impression — the  seven  coloured  rays  being 
perceived  all  at  once,  rather  than  one  after  another. 
Hence  the  circle  seemed  to  be  devoid  of  any  one  of 
the  colours  painted  upon  it,  and  to  partake  of  that 


428 


THE  WONDERS  OF  SCIENCE. 


white  tint  which  naturally  results  from  the  blending 
of  the  whole. 

Humphry  himself  was  almost  as  delighted  as  his 
sister  with  the  result  of  his  experiments.  It  was  de- 
monstrable that  the  light  of  the  sun  which  fills  the 
air  by  day,  and  seems  absolutely  colourless  to  us,  is 
not  of  that  simple  homogeneous  nature  which  we  are 
naturally  led  to  believe,  but  really  made  up  of  seven 
coloured  rays,  which  the  eye  itself  is  unable  to  sep- 
arate, and  from  which  proceed  all  the  several  hues 
with  which  the  earth  is  painted,  for  the  composite 
white  beam  falling  upon  the  different  objects  around 
is  broken  up  by  them  into  its  elementary  tints,  and 
some  one  of  these  reflected  by  them  to  us,  so  that  the 
object  itself  naturally  appears  of  the  same  colour  as 
the  beam  it  sends  to  the  eye. 

Humphry  had  now  to  investigate  the  several  prop- 
erties of  the  spectrum  itself 

It  will  be  remembered  that  he  before  found  the 
point  of  greatest  heat  to  exist  at  the  very  extremity 
of  the  red  ray,  and  he  now  ascertained  by.  means 
of  a photometer  (or  an  instrument  for  measuring  the 
relative  intensity  of  different  lights)  that  the  point  of 
greatest  light  existed  at  the  boundary  of  the  orange 
and  the  yellow  rays.  Consequently,  as  the  red  (or 
calorific)  rays  were  less  refrangible  than  the  yel- 
low (or  luminous)  rays,  there  was  but  one  conclusion 
to  come  to  — • light  teas  itself  more  refrangible  than 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY.  429 

heat;  that  is  to  say,  the  light  in  passing  through 
the  prism,  and  being  there  separated  from  the  heat 
with  which  it  was  previously  associated,  was  bent 
farther  out  of  its  course  than  the  heat  was,  so  that 
the  two  principles  were  differently  acted  upon  by 
the  glass,  and  consequently  possess  different  powers 
and  susceptibilities. 

“But  if,”  said  Humphry,  “the  red  rays  are  the 
calorific  ones,  and  the  yellow  rays  the  luminous 
ones,  what  peculiar  properties  belong  to  the  rays  at 
the  upper  end  of  the  spectrum,  where  the  sunbeam 
is  bent  the  farthest  of  all  out  of  its  previous  course  ? 
What  special  power  appertains  to  the  violet  and  blue 
portion  of  the  coloured  image  ?” 

The  youth  knew,  from  the  books  he  had  studied 
upon  the  subject,  that  these  constituted  the  chem- 
ical beams — that  is  to  say,  the  violet  extremity  of 
the  spectrum  had  been  found  to  possess  the  power 
of  separating  silver  from  some  of  its  compounds,  and 
Humphry  was  now  anxious  to  observe  the  effect  for 
himself. 

Having  brushed  a paper  over  with  a solution  of 
nitrate  of  silver  (lunar  caustic),  he  placed  a strip  of 
it  a little  way  beyond  the  violet  extremity  of  the 
spectrum ; another  strip  he  deposited  in  the  violet 
ray  itself ; a third  was  left  in  the  blue  ray ; while 
in  each  of  the  other  coloured  portions  a piece  of  the 
same  paper  was  exposed,  and  the  light  admitted  to 
them  all  at  the  same  time. 


430 


THE  WONDERS  OP  SCIENCE. 


It  was  then  found  that  the  nitrate  of  silver 
darkened  the  most  rapidly  at  that  part  of  the  spec- 
trum a little  beyond  the  violet  extremity — that  the 
chemical  effect  was  the  greatest  after  this  in  the 
violet  ray  itself.  Next,  the  blue  ray  possessed  a 
greater  decomposing  power  than  the  green ; whilst 
in  the  yellow  and  red  rays  no  such  power  was  per- 
ceptible, for  the  solution  of  silver  remained  un- 
darkened there. 

u So,  then,”  cried  Humphry,  “ the  wonderful 
sunbeams  that  stream  every  day  upon  the  earth 
contain  not  only  all  the  colours  of  the  rainbow,  but 
three  distinct,  subtle  principles,  locked  up  in  them 
— heat,  light,  and  chemical  influence ; each  of 
these  being  differently  refrangible  and  existing  in 
a ray  of  a different  colour;  the  heat  inhering  in 
the  red  or  lower  portion  of  the  spectrum,  and  the 
chemical  power  in  the  violet  or  opposite  extremity, 
whilst  the  light  occupies,  as  it  were,  a middle  place, 
residing  principally  in  the  yellow  portion.” 

Humphry  then  delighted  his  sister  by  preparing 
different  chemical  solutions,  to  be  acted  upon  by  the 
violet  rays  of  the  sun.” 

First,  he  made  some  chloride  of  silver  by  steep- 
ing a paper  in  salt  and  water  and  then  brushing 
it  over  with  a solution  of  lunar  caustic.  This  he 
found  to  darken  even  more  rapidly  than  the  nitrate 
of  silver  itself,  and  he  then  set  to  work  to  ascertain 
the  cause. 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY.  431 

Now  chloride  of  silver  lie  knew  to  consist  of  chlo- 
rine (a  green  coloured  gas)  and  silver,  and  he  was 
anxious  to  see  whether  light  would  act  upon  chlo- 
rine more  powerfully  than  it  did  upon  nitric  acid, 
as  Mr.  Wedgwood  had  told  him. 

Accordingly  he  filled  a jar  with  equal  portions  of 
hydrogen  and  chlorine  gases,  and  submitted  this  to 
the  action  of  the  sun’s  rays,  when,  to  the  astonish- 
ment of  himself  and  terror  of  Kitty,  the  jar  was  no 
sooner  placed  in  the  sunshine  than  the  two  gases 
detonated  with  the  noise  of  the  report  of  a pistol, 
and  the  jar  itself  was  almost  shivered  to  pieces  in 
the  explosion. 

Delighted  with  the  result,  and  anxious  to  re- 
peat the  experiment  in  a less  dangerous  form, 
he  filled  a tube,  about  half  an  inch  in  diameter 
and  twelve  inches  long,  with  the  same  gases,  and 
while  the  end  of  the  tube  was  inserted  in  a vessel 
of  water,  the  upper  part  of  it  was  shaded  with  an 
opaque  cover,  so  that  by  removing  this  for  an  in- 
stant he  could  allow  the  gases  within  the  tube  to  be 
acted  upon  by  the  light  for  as  short  a time  as  he 
pleased. 

In  this  manner  the  ingenious  youth  found,  that 
the  moment  the  opaque  cover  was  removed  and  the 
tube  exposed,  even  to  the  diffused  light  of  day,  a 
cloudiness  appeared  within  it,  owing  to  the  in- 
stantaneous, though  silent,  combination  of  the  two 
gases,  while  the  water  rose  more  or  less  rapidly 


432 


THE  WONDEKS  OF  SCIENCE. 


within  it  according  to  the  intensity  of  the  light. 
The  effect  even  of  a passing  cloud  was  thus  dis- 
tinctly seen  to  retard  the  rapidity  of  the  combina- 
tion, while,  when  exposed  to  the  full  solar  light, 
the  union  of  the  two  was  so  instantaneous  that 
the  gases  suddenly  disappeared  from  the  tube,  and 
the  water  rushed  violently  up  into  it  to  fill  the 
vacuum. 

Next  Humphry  found  that  the  two  gases,  when 
exposed  to  the  sun’s  rays  in  a tube  of  violet-colour- 
ed glass,  combine  rapidly,  but,  strange  to  say,  with- 
out explosion ; whereas  when  they  are  submitted  to 
the  action  of  sun-light  in  a tube  of  red  glass,  the 
gases  scarcely  act  upon  one  another.  It  was,  more- 
over, ascertained,  that  when  standing  in  a perfectly 
dark  place,  the  two  gases  do  not  enter  into  combina- 
tion in  any  length  of  time. 

The  lad  could  now  understand  why  the  chloride 
of  silver  darkened  so  rapidly  in  the  sun’s  rays. 
The  chlorine  with  which  the  metal  was  combined 
was  attacked  by  the  moisture  in  the  atmosphere, 
and  as  this  moisture  consisted  of  oxygen  and  hy- 
drogen in  the  form  of  water,  the  hydrogen  of  it 
was  made  by  the  chemical  influence  of  the  sun- 
beam to  enter  into  rapid  combination  with  the 
chlorine,  and  thus  the  silver  was  left  behind,  but 
in  such  minute  particles  that  the  metal,  instead  of 
appearing  white  as  it  usually  does,  assumed  the  form 
of  a black  powder,  which,  being  fixed  in  the  paper, 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY.  433 

naturally  caused  it  to  darken  in  those  parts  where 
the  light  had  fallen  upon  it. 

Filled  with  the  knowledge  he  had  thus  obtained, 
Humphry  set  to  work  to  produce  some  sun-pictures 
for  his  sister.  Patterns  of  pieces  of  lace  were  thus 
made  to  impress  their  forms  in  a few  seconds  upon 
paper  that  had  been  prepared  over-night  with  a coat- 
ing of  chloride  of  silver.  Where  the  light  fell,  the 
silver  was  separated  from  the  chlorine,  and  precipi- 
tated in  minute  black  particles,  so  that  the  paper 
was  darkened  in  those  parts;  while  in  the  places 
where  the  threads  of  the  lace  prevented  the  rays 
from  reaching  the  paper,  the  solution  was  undecom- 
posed, so  that  a white  line  exactly  corresponding  to 
the  pattern  of  the  lace  itself  became  impressed  upon 
the  black  ground. 

Kitty  was  overjoyed  at  the  first  picture  she  be- 
held her  brother  produce  by  the  light,  and  Hum- 
phry smiled  as  he  saw  her  take  it  to  the  window  to 
examine  it  more  minutely,  for  he  knew  that  as  she 
looked  at  it  the  light  would  begin  to  act  upon  the 
parts  that  had  been  previously  screened  by  the  lace 
itself,  and  where  the  solution  still  remained  unde- 
composed in  the  paper;  and  sure  enough,  in  a few 
minutes,  she  gradually  saw  the  pattern  vanish,  and 
the  whole  ultimately  become  of  one  uniform  dark- 
brown  tint. 

“What  a pity,”  cried  the  girl,  “that  so  beautiful 
a thing  should  be  so  perishable  ! If  you  could  only 

Ek 


434 


THE  WONDERS  OF  SCIENCE. 


find  out,  Humphry,  how  to  fix  the  pictures,  what  a 
great  thing  it  would  be  for  you  to  do !” 

The  brother  told  her,  that  in  order  to  accomplish 
this  it  was  necessary  to  discover  some  substance  that 
would  remove. the  undecomposed  chloride  of  silver, 
forming  the  white  parts  of  the  picture,  and  which 
would  not  attack  the  decomposed  silver  itself,  form- 
ing the  dark  parts  of  it. 

To  attain  this  end,  the  young  chemist  made  an  in- 
finity of  experiments,  but  without  avail ; for  though 
he  tried  a number  of  acids  and  alkaline  solutions,  he 
could  find  no  liquid  that  would  remove  the  unde- 
composed chloride  from  the  paper,  and  after  weeks 
of  toil  and  disappointment  he  was  obliged  to  con- 
fess, unwillingly,  that  the  difficulty  was  one  he  lack- 
ed the  power  to  master. 

Many  years  after  Davy’s  time,  however,  it  was 
discovered  that  the  chemical  substance  termed  hypo- 
sulphite of  soda  readily  dissolves  chloride  of  silver, 
and  has  little  or  no  action  upon  the  precipitated 
silver  itself ; and  from  this  period  may  be  dated  the 
perfection  of  the  wonderful  art  of  photography  (or 
sun-painting)  that  Thomas  Wedgwood  was  the  first 
to  attempt,  and  at  which  Davy  himself  was  one  of 
the  early  but  unsuccessful  experimenters. 

Of  this  art  there  are  now  two  distinct  branches, 
viz.  one  in  which  the  pictures  are  produced  upon 
metal,  the  other  upon  paper  or  glass.  In  the  me- 
tallic process,  iodide  of  silver  is  the  chemical  agent 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY.  435 

rather  than  the  chloride;  this  is  formed  by  sub- 
mitting a perfectly  clean  plate  of  polished  silver  to 
the  action  of  the  vapour  of  iodine,  and  sometimes 
to  bromine  afterwards,  in  order  to  quicken  the  ac- 
tion. The  plate  thus  prepared  is  placed  in  the 
camera,  so  that  an  image  of  the  object  to  be  copied 
may  fall  upon  it ; the  consequence  is,  that  in  the 
“lights”  of  the  picture  the  iodide  of  silver  becomes 
decomposed,  the  iodine  itself  going  off  in  the  form 
of  hydriodic  acid  gas,  by  combining  with  hydrogen 
in  the  moisture  of  the  air,  and  the  pure  silver  being 
left  behind ; whereas  in  the  shades  of  the  picture 
where  no  light  reaches,  the  iodide  of  silver  remains 
undecomposed.  The  action  usually  takes  place  in 
some  few  seconds,  according  to  the  intensity  of  the 
light  and  the  nature  of  the  “quick”  used.  When 
the  plate  is  removed  from  the  camera  no  picture 
is  visible  upon  its  surface,  so  that  the  developing 
part  of  the  process  has  then  to  be  performed.  This 
consists  in  submitting  the  plate  to  the  fumes  of  mer- 
cury, which  attach  themselves  to  the  parts  where 
the  pure  silver  has  been  separated  from  the  iodine 
with  which  it  was  combined.  These  parts  con- 
stitute, as  we  said  before,  the  “lights”  of  the  pic- 
ture, and  there  the  mercurial  vapour  is  condensed, 
and  clings  in  the  form  of  minute  globules ; whilst 
to  the  parts  which  have  been  undecomposed  the 
mercury  does  not  attach  itself,  having  no  affinity 
whatever  with  the  iodide  of  silver  that  remains  there. 


486 


THE  WONDERS  OF  SCIENCE. 


The  consequence  is,  the  globules  of  mercury  which 
cling  to  the  portions  where  the  rays  have  fallen, 
reflect  so  much  light  to  the  eye  that  they  form 
the  “ whites”  of  the  picture ; whereas  the  undecom- 
posed iodide  of  silver,  sending  no  light  to  the  ret- 
ina, constitutes  the  “ blacks and  thus  the  im- 
age, which  was  latent  on  the  plate,  is  developed, 
or  brought  out,  with  such  marvellous  fidelity,  that 
when  examined  with  a microscope,  characters  that 
were  several  miles  distant  in  the  original  may  be 
clearly  read  in  the  minute  sun-copy. 

After  this  comes  the  fixing  process,  and  that  con- 
sists merely  in  submitting  the  plate  to  the  action 
of  hyposulphite  of  soda , which  dissolves,  and  so  re- 
moves all  the  undecomposed  iodide  of  silver  from  it, 
and  thus  renders  it  incapable  of  being  further  acted 
upon  by  the  light. 

The  above  constitutes  what  is  now  usually  known 
as  the  “ Daguerreotype  process.” 

The  production  of  photographic  pictures  upon 
paper,  on  the  other  hand,  forms  what  is  termed  the 
u Talbotype  process” — -the  names  of  the  two  types 
being  derived  from  those  of  their  inventors.  In 
the  latter  method  of  producing  sun-pictures  there 
are  almost  the  same  different  stages  to  be  gone 
through.  The  paper  itself  has  first  to  be  iodised, 
or  rendered  sensitive  to  the  action  of  light,  by 
means  of  coating  it  with  a surface  of  iodide  of 
silver.  This  is  done  by  washing  it  over  first  with 


THE  WONDERS  OP  COLOUR  AND  PHOTOGRAPHY.  437 

a solution  of  nitrate  of  silver,  and  when  this  is  dry, 
with  a solution  of  iodide  of  potassium;  the  conse- 
quence is,  the  one  solution  decomposes  the  other, 
so  that  nitrate  of  potash  and  iodide  of  silver  are 
formed.  The  nitrate  of  potash,  being  soluble,  is 
then  washed  out  of  the  paper,  while  the  insoluble 
iodide  of  silver  remains  fixed  in  it.  Then  follows 
the  “ quickening ” part  of  the  process.  This  consists 
in  washing  the  sheet  of  iodised  paper  over  with  a 
solution  of  what  is  termed  gallo-nitrate  of  silver, 
which  consists  of  a small  proportion  of  gallic  acid 
(the  acid  from  gall-nuts)  dissolved  in  water,  and 
added  to  a solution  of  lunar  caustic,  having  a little 
acetic  acid,  or  pure  vinegar,  in  it.  The  gallic  and 
acetic  acids  are  used  because  it  is  found  that  the 
presence  of  any  vegetable  or  organic  matter  hastens 
the  decomposition  of  nitrate  of  silver  when  exposed 
to  light.  The  paper  is  now  ready  for  the  camera, 
and  is  so  sensitive  to  the  action  of  light  that  it 
is  said  to  transcend  the  ordinary  iodised  paper  in 
this  respect  more  than  a hundredfold,  so  that  even 
a second  or  two  of  time  is  sufficient  to  impress  a 
latent  image  upon  it. 

Then,  as  in  the  daguerreotype  method,  the  devel- 
oping process  has  to  be  resorted  to  in  order  to  bring 
out  the  picture,  which  is  imperceptible  on  remov- 
ing the  paper  from  the  camera,  and  the  existence 
of  which  would  not  be  suspected  by  any  one  who 
had  not  been  forwarned  of  it  by  previous  experi- 


438 


THE  WONDERS  OF  SCIENCE. 


ments.  To  render  the  picture  visible,  the  paper  is 
washed  over  once  more  with  the  gallo-nitrate  of 
silver  before  described,  and  then  warmed  gently 
before  the  fire  ; whereupon  that  part  of  the  paper 
upon  which  the  light  has  acted  begins  to  darken, 
while  the  other  part  of  the  paper  retains  its  white- 
ness. After  this,  as  in  the  u Daguerreotype”  meth- 
od, the  fixing  process  has  to  be  resorted  to.  This, 
for  “ Talbotypes,”  consists  in  washing  the  paper  in 
bromide  of  potassium,  which  dissolves  out  all  the  un- 
decomposed chemicals,  and  so  leaves  an  indelible  im- 
pression behind. 

The  picture  thus  produced,  however,  is  what 
is  termed  a “negative”  one — that  is  to  say,  the 
lights  in  the  original  are  represented  by  shades  in 
the  photographic  copy,  and  vice  versa , the  shades 
in  nature  are  rendered  as  lights  in  the  picture. 
The  Taibotype,  therefore,  lias  to  be  again  copied, 
in  order  that  the  lights  and  shades  may  be  accu- 
rately represented.  For  this  purpose,  however, 
the  paper  need  not  be  so  highly  sensitive ; so 
that  the  ordinary  quickening  part  of  the  process  by 
means  of  the  gallo-nitrate  may  be  dispensed  with, 
or  the  paper  may  be  coated  with  chloride  of  silver 
instead  of  the  iodide  before  described.  Again,  the 
developing  process  is  no  longer  necessary,  the  pic- 
ture being  produced  directly  by  the  action  of  light, 
rather  than  indirectly  by  means  of  some  developing 
agent.  Tli e,  fixing  process  in  this  stage  is  usually 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY.  439 

performed  by  means  of  hyposulphite  of  soda,  and 
by  these  means  the  negative  picture  before  pro- 
duced is  rendered  positive,  and  the  lights  and  shades 
thus  made  an  accurate  representation  of  those  in 
nature. 

It  will  now  be  seen  that  the  art  of  producing 
sun-pictures,  whether  by  the  Daguerreotype  or  the 
Talbotype,  comprises  usually  four  distinct  process- 
es, viz. : 

1.  The  preparatory  process,  which  consists  in 
preparing  the  plate  or  paper  — that  is  to  say,  in 
coating  it  with  some  solution  of  silver  that  is 
capable  of  being  decomposed  by  the  action  of 
light. 

2.  The  quickening  process,  which  consists,  again, 
in  rendering  the  plate  or  paper  more  highly  sensi- 
tive to  light  by  the  addition  of  some  other  chemical, 
which  facilitates  the  decomposition  of  the  compound 
of  silver,  with  which  the  surface  has  been  previously 
coated. 

3.  The  developing  process,  which  consists  in  ren- 
dering visible  the  latent  picture  which  has  been  im- 
pressed upon  the  plate  or  paper  while  exposed  to 
the  action  of  the  light  in  the  camera. 

4.  The  fixing  process,  or  the  dissolving  out  of 
all  the  undecomposed  silver  compound,  and  so  pre- 
venting the  light  from  having  any  further  action 
upon  it. 

Now  it  must  not  be  supposed  that  the  com- 


440 


THE  WONDERS  OF  SCIENCE. 


pounds  of  silver  are  those  only  which  are  capable 
of  being  decomposed  by  the  sun’s  rays,  for  photo- 
graphic pictures  have  been  produced  by  compounds 
of  all  the  precious  metals — such  as  gold,  platinum, 
mercury,  &c.,  these  substances  having  but  slight 
affinities,  and  so  being  easily  separable  from  the 
elements  with  which  they  are  united.  Again,  iron 
has  been  used  successfully  for  the  same  purpose — 
for  this  body,  also,  is  readily  decomposed  when  com- 
bined with  certain  substances.  Further,  the  gum- 
resins  and  bitumens  admit  of  being  employed  in 
the  same  manner,  and  many  vegetable  juices  have 
been  used  by  Sir  John  Herschel  for  a like  purpose. 
Indeed  it  has  been  truly  said,  that  almost  every 
substance  in  nature  is  affected,  in  some  way  or  oth- 
er, by  the  solar  rays,  for  we  now  know  that  no  sub- 
stance can  be  exposed  to  the  sun’s  rays  without  un- 
dergoing chemical  action. 

The  changes,  therefore,  that  are  continually  oc- 
curring in  the  external  world  are  quickened  by  the 
rays,  which  at  one  time  it  was  believed  gave  only 
light  and  heat  to  the  globe  that  we  inhabit;  and 
even  the  very  changes  of  the  seasons,  the  growth 
of  vegetation,  the  blossoming  of  the  flowers,  and 
the  ripening  of  the  fruits,  are  all  due,  in  a measure, 
to  the  chemical  influence  of  those  elementary  rays 
which  lie  concealed  in  the  compound  sunbeam : 
for  it  has  been  proved  that  the  sunshine  itself  is 
necessary,  even  to  the  breathing  of  plants  through 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY.  441 

their  leaves,  and  that  in  the  shade  they  cease  ab- 
sorbing the  carbon  from  the  atmosphere  which  is 
ultimately  destined  to  form  part  of  their  woody 
structure.  Thus  light  becomes  not  only  the  source 
of  beauty  to  the  world,  and  the  agent  upon  which 
one  of  our  most  wondrous  senses  depends,  namely, 
that  by  which  we  are  enabled  to  recognise  the 
form  and  nature  of  objects  at  a distance  from  us, 
but  it  is  also  the  source  of  health  and  vigour  to 
our  frames,  by  maturing  the  products  of  the  earth 
upon  which  we  live,  as  well  as  by  promoting  in 
our  own  frames  those  subtle  chemical  changes,  by 
which  our  bodies  are  nourished  and  our  faculties 
developed,  since  in  darkness  men  can  no  more  thrive 
than  plants. 

Had  Davy  lived  to  see  the  development  of  the 
chemical  influence  of  light  that  has  been  opened  up 
to  us  since  his  time,  he  would  have  been  the  loudest 
in  his  praises  of  the  marvels  wrought  by  it,  and, 
doubtless,  among  the  foremost  to  have  extended 
our  knowledge  of  its  action.  But  these  are  dis- 
coveries made  since  his  time,  and  discoveries  which 
he,  with  his  deep  insight  into  Nature,  was  unable 
to  foresee,  or  even  to  assist.  To  such  perfection, 
however,  has  the  photographic  art  been  carried 
since  the  days  when  Davy  vainly  essayed  to  fix  the 
images  which  took  him  some  quarter  of  an  hour  to 
produce,  that  not  only  can  stationary  objects  have 
their  forms  indelibly  impressed  upon  paper  by  the 


442 


THE  WONDERS  OF  SCIENCE. 


very  light  itself  which  renders  those  forms  visible  to 
us,  but  the  passing  shadows  that  give  beauty  to  the 
landscape  can  be  made  permanent,  the  very  undu- 
lation of  the  corn  can  be  seized,  the  rustling  of  the 
leaves  detained,  and  even  the  rippling  of  the  waters, 
the  playing  of  the  fountains,  and  the  curling  of  the 
smoke,  whose  particles  never  for  two  moments  to- 
gether remain  in  the  same  place,  can  be  arrested,  and 
their  evanescent  forms  painted  by  themselves,  as  it 
were,  upon  the  tablets ; so  that  the  effect  of  a mere 
instant  can,  by  its  marvellous  agency,  be  prolonged 
for  years.  Thus  time,  which  is  known  to  us  only 
by  the  changes  which  are  continually  occurring  with- 
out and  within  us,  has  all  the  fixity  of  space ; and 
those  historical  events  which  our  forefathers  were 
unable  to  convey  to  us,  from  the  want  of  some  such 
art,  can  now  be  handed  down,  rendered  with  all 
the  truth  of  light  itself,  so  that  future  generations 
gazing  at  them  may  behold  the  same  scenes  that 
were  impressed  at  the  back  of  our  eyes  years  be- 
fore. Indeed,  the  photographic  art  itself  is  but  the 
process  of  individual  and  transient  vision  made  uni- 
versal and  permanent ; for  the  eye  itself  is  but  the 
camera  through  which  we  gaze  at  the  world  with- 
out, and  the  retina  at  the  back  of  the  organ  of  sight 
no  more  than  a photographic  plate,  as  it  were,  im- 
pressing the  images  that  flit  before  our  vision  more 
or  less  permanently  upon  our  memories. 

As  an  instance,  however,  of  the  perfection,  we  re- 


THE  WONDERS  OF  COLOUR  AND  PHOTOGRAPHY.  443 

peat,  to  which  this  process  of  fixing  the  most  tran- 
sient images  has  been  carried,  we  need  only  mention 
the  experiment  performed  by  Mr.  Talbot,  in  which 
a moving  body,  that  was  made  to  revolve  at  an  enor- 
mous speed,  and  that  was  illuminated  but  for  an  in- 
stant by  the  electric  spark,  was  photographed  as  a 
stationary  object.  * 

It  is  well  known  that  a wheel  revolving  at  a rap- 
id rate  is  barely  visible  to  us,  the  spokes  passing 
with  such  velocity  before  the  eye  that  we  are  un- 
able to  distinguish  one  from  the  other,  so  that  the 
whole  appears  to  us  almost  as  one  entire  disc ; such 
a wheel,  however,  if  made  to  rotate  in  the  dark,  and 
then  suddenly  illuminated  for  that  inappreciable  por- 
tion of  time  which  the  electric  spark — the  miniature 
lightning  of  the  laboratory — endures,  then  appears 
to  us  as  if  absolutely  standing  still ; for  as  we  see  it 
under  such  circumstances  only  in  that  place  which 
it  occupies  so  long  as  the  light  lasts,  and  this  being 
but  for  the  least  conceivable  term  of  duration,  it  has 
no  time — however  rapidly  it  may  be  turning  on  its 
axis — to  pass  from  one  point  of  space  to  another,  so 
that  it  can  but  appear  to  us  as  if  utterly  stationary. 

In  the  experiment  we  allude  to,  a wheel  was  thus 
made  to  revolve  so  rapidly,  that  its  revolutions 
were  counted  by  the  musical  note  produced  by  the 
vibrations  of  a spring,  that  moved  backwards  and 
forwards  once  at  each  turn.  The  revolutions  were 
performed  in  the  dark ; and  during  this  the  chain- 


444 


THE  WONDERS  OF  SCIENCE. 


ber  and  wheel  were  suddenly  lighted  by  one  spark 
drawn  from  a powerful  electric  machine.  At  this 
moment  a photographic  apparatus  was  presented  to 
the  wheel  itself,  and  on  developing  the  image  thus 
produced  upon  the  paper  which  had  been  previous- 
ly inserted  in  the  camera,  it  was  found  to  be  im- 
pressed with  a perfect  copy  of  the  wheel  itself,  with 
all  its  spokes  distinctly  visible,  and  precisely  the 
same  as  if  the  image  had  been  taken  from  the  wheel 
while  in  a state  of  rest.  It  was  the  same  stationary 
image,  too,  as  the  spectators  themselves  had  beheld 
during  the  instantaneous  illumination  of  the  object ; 
and  thus,  by  the  aid  of  the  same  fluid  as  the  light- 
ning itself,  and  with  the  assistance  of  music  to  reg- 
ister the  rate  of  revolution,  that  mysterious  princi- 
ple of  motion  which  has  puzzled  philosophers  since 
philosophy  began,  was  made  to  appear  like  rest,  and 
even  the  sensibility  of  the  eye  itself  rivalled  by  pho- 
tographic agency,  so  that  the  dead  paper  was  made 
to  be  impressed  with  the  very  same  figure  as  the  liv- 
ing retina  itself  perceived. 


CHAPTER  XYHI. 


CONCLUSION. 

During  the  prosecution  of  his  later  experiments 
Humphry  had  formed  the  acquaintance  of  Mr.  Da- 
vies Giddy,  a gentleman  of  high  scientific  attain- 
ments, better  known  under  the  name  of  Davies  Gil- 
bert, and  who  was  then  resident  at  Tredrea,  near 
Penzance. 

This  gentleman,  who  ultimately  became  Presi- 
dent of  the  Royal  Society,  proved  of  great  service 
to  young  Davy,  for  not  only  did  he  lend  the  boy 
such  apparatus  as  he  required  for  the  carrying  out 
of  his  experiments,  but  he  delighted  to  converse 
with  Humphry;  and  though  he  could  not  help 
smiling  occasionally  at  the  strangeness  of  his  theo- 
ries, he  grew  to  have  a lively  sense  of  the  ardour  of 
the  youth’s  imagination,  and  the  originality  of  his 
mind. 

Now  it  so  happened  that  Davies  Giddy  was 


446 


THE  WONDERS  OF  SCIENCE. 


acquainted  with  Dr.  Beddoes,  who  had  formerly 
been  one  of  the  Oxford  Professors,  but  who  had 
recently  opened  a Pneumatic  Institution  at  Bristol 
for  the  cure  of  diseases  by  the  inhalation  of  gases ; 
and  it  was  during  one  of  Dr.  Beddoes’  visits  to 
Davies  Giddy  that  Humphry  made  the  acquaint- 
ance of  the  Doctor,  and  so  favourable  an  im- 
pression did  he  make  upon  the  gentleman,  that 
not  long  afterwards  a letter  was  sent,  offering 
Humphry  the  post  of  Assistant  to  the  Bristol  In- 
stitution. 

The  lad  was  delighted  at  the  prospect  of  re- 
moving from  so  remote  a place  as  his  native  town, 
and  lost  no  time  in  talking  the  matter  over  with 
his  friends.  Mr.  Giddy  told . him  of  the  Doctor’s 
influence,  and  how  his  Institution  was  already  the 
resort  of  some  of  the  most  eminent  persons  in  the 
country,  and  warmly  advised  him  to  avail  himself 
of  the  offer. 

Mr.  Borlase,  to  whom  Humphry  repeated  all  that 
Mr.  Giddy  had  said,  counselled  the  boy  to  take  the 
same  step,  and  added,  that  he  had  been  so  pleased 
with  his  conduct  while  under  his  roof  that  he  would 
in  no  way  impede  his  advancement,  but  would  rath- 
er cancel  his  indentures,  even  though  he  was  just 
beginning  to  be  of  service  to  him. 

Mrs.  Davy,  too,  was  anxious  that  her  boy — 
whom  she  felt  more  and  more  convinced  was  des- 
tined to  take  a high  rank  in  the  world  — should 


CONCLUSION. 


447 


be  transferred  to  a wider  sphere,  where  his  abilities 
would  have  greater  chance  of  being  called  into  play, 
and  she  gladly  accompanied  Humphry  to  their  old 
friend,  Mr.  Tonkin,  to  break  the  matter  to  him,  and 
hear  what  he  thought  of  the  proposal. 

The  old  gentleman,  however,  could  not  be  made 
to  listen  to  the  project,  and  did  not  hesitate  to  de- 
nounce Humphry’s  desire  for  worldly  honour  as  the 
“ wild-goose  chase”  which  led  many  an  ambitious 
simpleton  astray,  saying,  that  if  the  boy  would 
make  up  his  mind  to  settle  in  his  native  place,  he 
might  be  assured  of  a comfortable  independence, 
for  he  would  find  but  few  able  to  compete  with 
him  there.  Nevertheless,  in  a large  town — how- 
ever striking  his  talents  might  appear  in  a small 
one — the  circle  of  his  competitors  would  be  so  much 
increased,  that  he  would  sink  into  a mere  nobody, 
and  end  his  days  as  one  of  the  many  fools  who 
had  struggled  after  the  world’s  prizes,  and  found, 
when  too  late,  that  there  was  no  chance  of  obtain- 
ing them. 

Mrs.  Davy,  however,  mother-like,  felt  satisfied 
that  Mr.  Tonkin  took  an  erroneous  view  of  her 
son’s  powers,  and  she  strove  to  assure  her  old 
friend  that  he  did  not  know  what  Humphry  was 
capable  of  doing  so  well  as  she  did,  and  that  if  he 
did,  he  would  have  as  little  fear  as  herself  of  his 
failure. 

Mr.  Tonkin,  however,  was  not  to  be  argued  out 


448 


THE  WONDERS  OF  SCIENCE. 


of  the  notion  he  had  taken  up,  and  ultimately  grew 
so  annoyed  with  what  he  fancied  to  be  merely  a 
mother’s  silly  prejudice  on  Mrs.  Davy’s  part,  that 
he  ended  the  interview  by  vowing  that  the  boy 
should  never  quit  Penzance  with  his  consent. 

This,  for  a time,  put  a stop  to  the  correspondence 
on  the  subject.  At  length,  however,  Dr.  Beddoes 
became  so  urgent  that  Humphry  should  join  him, 
that,  despite  the  objections  of  Mr.  Tonkin,  who  still 
would  not  listen  to  the  plan,  his  friends  advised  him 
to  accept  the  offer ; and  it  was  accordingly  arranged 
that  young  Davy  should  leave  Penzance  as  soon  as 
he  conveniently  could. 

Accordingly,  on  the  2d  of  October,  in  the  year 
1798,  Humphry,  not  then  twenty  years  of  age,  quit- 
ted his  native  town  for  the  first  time  in  his  life,  and 
that  to  commence  fighting  his  way  in  the  world. 

His  mother  parted  from  him  as  full  of  high  hope 
as  the  boy  himself ; and  as  the  boy  hugged  the  wid- 
ow to  his  heart  alone  in  her  chamber,  before  he  left 
her,  he  said,  with  the  sobs  in  his  throat,  “ Mr. 
Tonkin  does  not  know  me,  mother,  yet:  but  be 
you  of  good  cheer,  I will  live  to  be  an  honour  and 
a glory  to  you  still ; and  it  shall  be  my  proud  lot  to 
say  some  day  that  I was  the  means  of  raising  you 
and  all  that  belong  to  me  to  a position  of  comfort 
and  eminence.  Years  ago  now,  mother,  I told  you 
I would  do  it,  and  the  resolve  is  still  deep  in  my 
heart.” 


CONCLUSION. 


449 


Mrs.  Davy  assured  him  she  had  every  confidence 
in  his  attaining  the  noble  object  he  had  in  view,  and 
she  parted  from  him,  though  with  tears  in  her  eyes, 
with  a smile  of  high  hope  upon  her  lip. 

Mr.  Tonkin,  however,  was  resolute  to  the  last,  and 
at  his  leave-taking  denounced  Humphry’s  plans  as 
visionary  schemes ; and  when  the  boy  had  left,  and 
the  old  gentleman  found  his  favourite  plan  of  set- 
tling Humphry  in  his  native  town  as  a surgeon  had 
been  thwarted,  he  altered  his  will,  and  revoked  the 
legacy  of  the  house  that  he  had  previously  bequeath- 
ed to  his  foster-son. 

On  young  Humphry’s  journey  to  Bath  he  met  his 
friend  Mr.  Davies  Giddy  at  Oakhampton,  and  while 
breakfasting  there,  the  mail-coach  from  London 
drew  up  at  the  door  of  the  inn,  covered  with  lau- 
rels and  ribbons,  and  bringing  the  first  news  of  Nel- 
son’s victory  of  the  Nile. 

“ I have  a greater  fight  than  that  to  fight,”  said 
Humphry  to  himself ; “ and,  please  God,  I will  gain 
the  victory,  too.” 

It  was  Mrs.  Davy’s  happy  lot  to  witness  the 
realisation  of  all  the  hopes  she  had  formed  of  her 
boy  in  his  youth ; for,  during  her  life,  he  rose  to  be 
elected  President  of  the  Royal  Society,  and  to  be 
created  a Baronet,  for  the  many  additions  he  had 
made  to  the  stock  of  knowledge;  to  be  rewarded 

F F 


450  THE  WONDERS  OF  SCIENCE. 

with  the  first  prize  instituted  by  the  Emperor  Napo- 
leon for  the  greatest  scientific  discovery  of  the  time ; 
and  to  be  allowed  a free  passage  through  France  at 
a time  when  all  other  Englishmen,  no  matter  how 
high  their  rank  or  character,  were  denied  admission 
into  that  country. 


INDEX. 


Aik,  currents  of,  how  caused,  1S6. 

Air-pump,  experiments  with,  236. 

Animal  mechanism,  wonders  of,  88. 

Argand-burners,  why  superior  in 
brilliancy,  300. 

Artificial  light  dependent  on  heat, 
297. 

Bath  wells,  temperature  of  the,  125. 

Blow-pipe,  cause  of  the  increased 
heat  produced  by  the,  300. 

Brocken,  spectre  of  the, in  the  Hartz 
mountains,  380;  philosophy  of," 
383. 

Camera,  images  produced  in,  342 ; 
why  reversed,  372 ; how  the  lens 
intensifies  images  in  the,  377 ; 
cause  of  variation  in  the  size  of 
objects  in,  378;  pictures  must  be 
projected  bn  an  opaque  body,  380. 

Cellini,  Benvenuto,  and  the  necro- 
mancer, 417. 

Chlorine,  experiments  with,  279. 

Coal,  power  concentrated  in,  110. 

Coal-mine,  destructive  explosion 
in,  94. 

Colours,  curious  result  from  mix- 
ing in  certain  proportions,  425. 

Combustion,  laws  of,  113 ; phenom- 
ena of,  245;  nature  of,  259;  ex- 
periments in,  247 ; philosophy  of, 
284. 

Combustion,  spontaneous,  262,  272. 

Corpse  candles , philosophy  of,  261. 

Creation,  the  wondrous  story  of, 
116. 

Daguerreotype  process  of  photog- 
raphy, 436. 

Dew,  deposition  of,  144 ; less  plen- 
tiful in  cloudy  weather,  146 ; its 
laws,  147. 

Drummond  light,  the,  296. 

Earthquakes,  126. 

Electric  light,  296. 

Ether,  its  powers  of  vaporization, 
224. 

Explosive  substances,  261,  264,  266. 

Eye,  the,  wonderful  construction 
of,  87. 


Fire-damp  not  inflammable  by  red 
heat,  273;  rapidly  explodes  at 
white  heat,  274;  explosible  only 
when  mixed  with  atmospheric 
air,  303. 

Flame,  subterranean,  125. 

Flame,  nature  of,  285,  293;  of  a 
candle  hollow,  298 ; experiments 
with,  301. 

Fluids,  expansive  power  of,  202. 

Fulminates  of  the  precious  metals, 
267 ; gold,  268 ; mercury,  268 ; 
silver,  269 ; platinum,  270. 

Gas,  its  first  application  to  illumin- 
ation, 109. 

Glass  absorbs  artificial , but  trans- 
mits solar  heat,  159. 

Hastings,  French  coast  sometimes 
visible  from,  by  refraction,  358. 

Heat,  natural  sources  of,  116;  ce- 
lestial, 118;  subterraneous,  120- 
124;  mechanical  production  of, 
129  ; chemical,  130 ; combustion, 
182 ; respiration,  131 ; communi- 
cation of,  134 ; radiation,  187 ; 
reflexion,  148;  difference  between 
solar  and  terrestrial , 15S ; trans- 
mission of,  158-161;  absorption 
of,  168;  degrees  of,  in  the  spec- 
trum, 162 ; relative  absorbing  and 
radiating  powers  of  surfaces,  165 ; 
radiation  by  different  colours, 
166 ; solar  more  powerful  reflect- 
ed than  direct,  168;  conduction, 
169 ; wonderful  effects  of,  193 ; 
expansive  power  of,  196;  latent, 
212;  white,  244;  artificial,  curi- 
ous changes  in  its  character  at 
high  rates  of  temperature,  244; 
then  assumes  all  the  properties 
of  solar,  244. 

Hot-springs  and  wells,  125. 

Ignes  fatui , how  produced,  260. 

Jack-o'-lanterns , causes  of,  260. 

Land’s  End  described,  41. 

Lens,  magnifying  power  of  the, 
how  determined,  391. 


452 


INDEX, 


Light,  electric,  296;  artificial,  de- 
pendent on  heat,  297 ; rays  of, 
travel  in  straight  lines,  844,  419 ; 
refraction  of,  850,  857 ; experi- 
ments, 851 ; rays  of,  assume  the 
colour  of  objects  from  which  they 
are  reflected,  867 ; reflexion  of, 
407 ; compound  nature  of  a ray 
of,  422;  composed  of  seven  col- 
ours, 428. 

Lightning,  varieties  of,  128. 

Liquids  imperfect  conductors  of 
heat,  177 ; merely  solids  whose 
particles  are  kept  apart  by  heat, 
212. 

Lucifer-matches,  why  so  readily  in- 
flammable, 272. 

Luminosity,  temperature  at  which 
bodies  assume,  248. 

Magician’s  mirror,  the,  explained, 
412. 

Mail-coaches,  the  first,  109. 

Metals,  their  relative  power  of  con- 
ducting heat,  172 ; expansion  and 
contraction  of,  197  ; practical  ap- 
plication of  this  power,  198 ; cool- 
ing of,  289. 

Microscope,  principle  of  the,  895, 
401 ; the  single,  397 ; the  com- 
pound, 400. 

Mirage , an  optical  illusion  caused 
by  refraction,  857. 

Mirrors,  concave,  experiments  with, 
148 ; wonders  produced  by,  418 ; 
different  effects  produced  by  me- 
tallic and  glass,  154. 

Mont  Blanc,  ascent  of,  110 ; ebulli- 
tion on  summit  of,  280. 

Objects,  why  they  diminish  in 
size  in  proportion  to  distance, 
886;  magnifying  of,  by  lenses, 
888. 

Oceanic  currents,  direction  of  the, 
190. 

Oils,  lamp,  philosophy  of  the  com- 
bustion of,  275,  295. 

Palissy,  Bernard,  his  discoveries  in 
pottery,  333. 

Pendulum,  compensation,  principle 
of  the,  200. 

Phlogiston,  an  imaginary  principle, 

245. 


Photography,  first  experiments  in, 
885,  433 ; practice  of,  435. 

Prism,  the  spectrum  produced  by, 
merely  an  oblong  figure  of  the 
sun,  421 ; its  colours  the  decom- 
position of  the  sunbeam  into  its 
elementary  tints,  422. 

Pyramids  of  Egypt,  size  of  the,  110. 

Pyxophorus,  how  produced,  261. 

Badiation,  power  of,  in  different 
substances,  142. 

Ramsgate,  Dover  Castle  rendered 
visible  from,  by  refraction,  860.  _ 

Refraction  of  light,  curious  prop- 
erty of,  857 ; illusions  caused  by 
extraordinary  instances  of,  858, 
360. 

Respiration,  philosophy  of,  86. 

Safety-lamp,  first  glimmer  of  the, 
93 ; experiments  with,  285 ; com- 
pletion of  the  first,  305 ; its  per- 
fected form,  311 ; value  and  im- 
portance of  the  invention,  803. 

St.  Michael’s  Mount,  Cornwall,  73. 

Science,  true,  its  nature,  87. 

Scoresby’s,  Captain,  observation  of 
a distant  ship  by  refraction,  865. 

Secretion,  marvels  of,  85. 

Spectrum,  proportions  of  prismatic 
tints  in  the,  426 ; circular,  427. 

Spontaneous  combustion,  262,  272. 

Steam,  difference  of  heat  in  high 
and  low  pressure,  178. 

Steam-boat,  the  first,  107. 

Sun-pictures,  the  earliest,  335. 

Talbot,  Mr.  Fox,  his  curious  exper- 
iment of  photographing  a rapidly 
revolving  wheel,  443. 

Talbotype  process  of  photography, 
436. 

Telescope,  principle  of  the,  893, 400. 

Temperature,  rate  of  increase  be- 
low the  surface  of  the  earth,  122. 

Vaporizable  liquids  readily  explos- 
ive, 274. 

^Vision,  range  of,  386. 

p v olcanoes,  126. 

Will-o'-the-wisp, philosophy  Of,  260. 

Wire-gauze,  its  power  of  resisting 
flame,  310. 


THE  END. 


I 


I 


1 ^ 

3^04- 


|HE GETTY  C£iV.c.:: 

LIBRARY 


